-NRLF 


VALVES,  VALVE-GEARS 
AND  VALVE  DIAGRAMS 


BY 


FRANKLIN   DER.   FURMAN,   M.E. 

<  * 

PROFESSOR   OF   MECHANISM   AND   MACHINE   DESIGN, 
STEVENS   INSTITUTE   OF   TECHNOLOGY 


ONE    HUNDRED   AND   FIFTY-TWO    ILLUSTRATIONS 


HOBOKEN,   N.   J. 
1911 


COPYRIGHT,  1911,  BY 
FRANKLIN    bicR.    FURMAN 


THK     TROW     PRBSS 
NK W     YORK 


PREFACE 

About  eight  years  ago  the  author  prepared  a  set  of  Notes  on  this  subject  and  they  have  since 
been  regularly  issued  and  revised  every  one  or  two  years  in  neostyle  form.  This  method  of  issuing 
notes  is  admirable  for  the  purpose  of  making  revisions  that  appear  to  be  desirable  after  a  course 
in  the  class  room,  and  the  author  would  be  reluctant  to  abandon  this  advantage  were  it  not  that 
the  well-established  points  of  the  subject  in  general  appear  to  be  in  such  shape  that  very  little  re- 
vision has  seemed  necessary  the  past  few  years. 

On  account  of  the  fact  that  about  twenty  per  cent,  of  new  material,  both  in  text  and  illustra- 
tions, has  been  added  this  summer  in  the  preparation  for  this  book,  the  author  feels  that  there  may 
be  some  revision  of  this  new  matter  desirable  after  it  has  been  tried  out  in  the  class  room,  and  has, 
therefore,  decided  to  publish  the  book  privately  and  in  small  editions  until,  at  least,  this  new  part 
of  the  subject  shall  become  as  settled  as  the  older  part.  A  further  prompting  for  issuing  these 
notes  in  book  form  is  the  fact  that  during  the  past  few  years  there  has  been  a  small  scattered  call 
from  graduates  who  have  not  kept  or  have  lost  their  loose-sheet  notes,  and  also  a  call  from  out- 
siders. Books  are  more  satisfactory  in  meeting  such  cases. 

Notes  on  this  subject  at  Stevens  Institute  were  started  by  Professor  Jacobus,  and  continued 
by  Professors  Anderson  and  Pryor,  until  the  subject  came  into  the  writer's  hands  in  1903.  The 
work  thus  started  was  part  of  a  more  general  course  in  engine  work  and  consisted  principally  of 
notes  leading  up  to  the  drafting-room  course,  cpvering  eight  problems  which  are  now  given  at 
pages  17,  28,  50,  54,  64,  82,  98  and  116.  Of  these  problems,  four,  comprising  the  double-ported, 
Meyer,  Corliss  and  floating  valves,  have  been  either  largely  revised  or  entirely  changed. 

The  material  in  this  book,  aside  from  the  drafting-room  problems,  has  been  arranged  for  class- 
room and  recitation  work  after  extended  visits  to  drafting  rooms  in  which  the  work  in  the  design 
of  valves  and  valve  gears  was  being  carried  on  in  a  practical  way,  and  it  is  believed  that  the  methods 
here  presented  will  be  found  to  agree  fairly  well  with  general  practice. 

While  an  arrangement  of  material  that  would  best  fit  in  with  the  general  course  of  mechanical 
engineering  at  Stevens  Institute  has  been  the  principal  aim  of  the  author  in  presenting  this  work, 
and  while  many  suggestions  from  numerous  sources,  including  the  works  of  Zeuner,  Bilgram,  Auchin- 
closs,  Welch,  Halsey,  Peabody,  Spangler  and  Begtrup,  have  been  adopted,  there  have  been  intro- 
duced some  features  that  have  been  original  in  their  conception  so  far  as  is  known  to  the  writer. 
Principal  among  these  may  be  mentioned  the  introduction  of  numbers  marking  the  order  of  the 
drawing  of  lines  in  the  construction  of  valve  diagrams  in  the  early  exercises,  thus  requiring 
synthetic  as  well  as  analytic  study  at  the  outset  of  the  course;  the  formula  for  determining 
exactly  the  steam-lap  by  the  Zeuner  diagram  when  port-opening,  lead  and  cut-off  are  given; 


268946 


iv  PREFACE 

the  introduction  of  preliminary  free-hand  problems  before  taking  up  the  regular  drafting-room 
problems;  the  combining  of  the  valve  ellipse  with  the  steam  engine  indicator-card  to  determine 
the  steam  and  exhaust  laps,  steam  and  exhaust  port  openings  and  lead  while  the  engine  is  in 
service,  or  without  removing  the  steam-chest  cover;  the  method  of  determining  the  proper  width 
of  cut-off  blocks  for  the  Meyer  valve;  the  Corliss  valve-gear  design,  and  the  condensed  arrange- 
ment of  Auchincloss's  method  of  design  of  the  Stephenson  link  motion. 

Among  the  recently  developed  methods  of  steam  control  that  have  been  included  are  the  Baker 
valve-gear  for  locomotives,  the  Lentz  gear  for  stationary  engines  and  the  Curtis  and  Westinghouse 
gears  for  steam  turbines. 

FRANKLIN  DER.  FURMAN. 

HOBOKEN,  N.  J.,  August  17,  1911. 


TABLE  OF  CONTENTS 

PAGE 

SECTION  I. — SIMPLE  STEAM-ENGINE  .  1 

Elements  of  Valves  and  Valve-Gears  .....  1 

Names  of  Engine  Parts 1 

Crank  End,  Head  End,  Forward  Stroke,  Return  Stroke,  Dead-Center     .        .  1 

"  Running  Over,"  "Running  Under "      ...                ...  1 

Operation  of  Steam-Engine 

Elementary  Steam  Valve   ...  2 

Steam-Lap,  Lap  Angle 

Lead,  Lead  Angle,  Angle  of  Advance      ...  3 

Exhaust-Lap ...  4 

Finite  and  "Infinite"  Connecting- Rods— Effect  of  Angularity  of  Finite  Rod         .  4 

Zeuner  Diagram 5 

Application  of  the  Zeuner  Diagram 7 

Principal  Phases  of  a  Steam-Engine  Cycle .  ,9 

Positive  and  Negative  Exhaust-Laps 9 

Exercise  Drills  in  the  Use  of  the  Zeuner  Diagrams       .        .        .        .        .        .        .        .10 

Exercise  Problems •                                             .  12 

Steam- Pipes,  Steam-Ports  and  Steam-Port  Opening         ,                               ....  13 

Distinction  Between  Port  Width  and  Port  Opening      ........  13 

Overtravel 13 

Formula  for  Calculating  Live  and  Exhaust  Steam-Ports     .        .                        ...  14 

Actual  and  Average  Velocity  of  Flow  of  Steam  Through  Ports          .        .                        .  14 

Note  Book  Problems .        .  .15 

Drafting  Table  Problem,  No.  1.— Plain  D- Valve      .  17 

Construction  of  Zeuner  Diagram .        .        .17 

Layout  of  Valve  and  Valve-Seat 18 

Formula  for  Minimum  Width  of  Bridge          .                        ......  19 

Formula  for  Width  of  Exhaust  Port        .  19 

Equalizing  Cut-Off s  by  Unequal  Steam- Laps 19 

Equalizing  Compression  by  Unequal  Exhaust-Laps — Special  and  General  Cases   .        .  19 

Equalization    of    Release    and    Exhaust-Closure    by  Unequal    Exhaust- Laps;    Special 

Case  ...  ....  .20 

Rocker- Arms,  Straight  and  Bent,  and  Their  Effect  on  Valve-Travel  and  Steam  Distribu- 
tion   .        .               ....  23 

Types  of  Rocker- Arms ....  23 

Equalizing  Cut-Off  by  a  Valve  Having  Equal  Steam- Laps ...                        .  23 

Unequal  Valve-Travel  on  Head  and  Crank  Ends  Due  to  Rocker       .                ...  25 
Zeuner  Circles  Changed  to  Irregular  Closed  Curves  by  Rocker          .                               .25 

v 


vi  CONTENTS 

PAGE 

SECTION  I.-— SIMPLE  STEAM-ENGINE — (Continued} 

Limited  Use  of  the  Plain  D-Valve       .  .       27 

Special  Valve  Exercise           .       .                                                     .  .28 

The  Allen  Valve        ...  .28 

Drafting  Table  Problem,  No.  2. — Design  for  an  Allen  Valve 28 

Effect  of  Two  Admission-  and  Two  Lead- Areas  on  Zeuner  Diagram  Construction        .       29 

Locomotive  Balanced  Valve      .  .31 

Limited  Use  of  the  Allen  Valve        .                       .  .31 

SECTION  II. — VALVE  DIAGRAMS  .  32 

Bilgram  Diagram .32 

Solution  of  Drafting  Table  Problem,  No.  1,  by  Bilgram  Diagram     .  .       33 

Reuleaux  Diagram .35 

Valve  Ellipse    ....  .35 
Method  of  Determining  Steam  and  Exhaust-Port  Openings,  and  Steam  and  Exhaust- 
Laps  by  Combining  the  Valve  Ellipse  and  Indicator  Cards,  and  Without  Removing 

Steam  Chest  Cover ....       36 

Sinusoidal  Diagram        ...                              .  .38 

SECTION  III. — TYPES  OF  VALVES       .                      .  .39 

Effect  of  Friction  Due  to  Pressure  on  Back  of  Plain  D- Valve  .        .       39 

Classification  of  Valves  ......               .       .  40 

One-Piece  Valves .40 

Valves  With  Two  or  More  Parts      ...                                      .  .40 

Piston-Valve        ....  .40 

Pressure-Plate  Valves .43 

Double-Ported  Valves  or  Their  Equivalent    ...  .47 

Valves  Which  Operate  by  Two  or  More  Independents  Parts     .  .47 

Two-Part  Valves .  47 

Drafting  Table  Problem,  No.  3.— Double  Ported  Valve  .  .       50 

Method  of  Computation  When  More  than  One  Port  is  Used     .  .       50 

Computation  for  Steam  Passageway  in  the  Valve  Itself      .  .53 

Area  of  Exhaust  Passageway  in  Cylinder       ...                              .  .53 

Drafting  Table  Problem,  No.  4. — Meyer  Valve        .  .       54 

To  Find  the  Auxiliary  Valve  Circle  C  K  and  C  L  .54 
To  Find  the  Relative  Valve  Circle  Showing  How  Far  the  Two  Valves  are  Apart  at 

any  Instant 55 

Explanation  of  the  Value  of  S  Which  Determines  the  Point  of  Cut-Off   ....       56 

Width  W  of  Cut-Off  Blocks      .               .  57 

Corliss  Valve-Gear .  .59 

Detail  and  Operation  of  Releasing  Gear .  .       60 

Limited  Range  of  Cut-Off  With  Single  Eccentric  .       61 

Setting  Corliss  Valve-Gear .62 

Drafting  Table  Problem,  No.  5. — Corliss  Valve-Gear      .        .  64 

Bent  Rocker  to  Neutralize  Angularity  of  Connecting-Rod         .  .       64 

Determination  of  Valve  Travel  for  Cylindrical  Rotating  Valve  .       65 

Determination  of  Travel  of  Piston  of  Dashpot      ...  .66 

Avoidance  of  Dead  Points  in  Valve-Gear  Mechanism         .  .67 

Examples  of  Practical  Valve  Construction ...  .68 


CONTENTS  vii 

PAGE 

SECTION  IV. — ECCENTRICS  AND  SHAFT  GOVERNORS       ...  .70 

Ec.centrics 70 

Classification  of  Eccentrics       .  70 

Reversing  With  Eccentrics 70 

Exercises  Showing  the  Relations  Between  Eccentric  Positions  and  Zeuner  Diagrams  .       70 

Examples  of  Practical  Eccentric  and  Governor  Construction .        .  .73 

Effect  of  Location  of  Pivot  in  Curved-Slot  Eccentrics ...  .       73 

Comparative  Indicator  Cards  from  Different  Kinds  of  Eccentrics .               .        .  .    .   79 

Shaft  Governors 81 

Effects  Produced  by  Rate  of  Rotation  and  by  Rate  of  Change  of  Rotation    .        .  .       81 

Throttling  Governors 82 

Drafting  Table  Problem,  No.  6. — Comparison  Results  from  Straight-Slot  and  Rotating 

.   Eccentrics .                              .  .82 

SECTION  V. — VALVE-GEARS  

Stephenson  Gear     .  ........  ... 

Method  of  Reversing         .  .  .  .  ... 

A  Valve-Gear  at  any  One  Setting  Equivalent  to  an  Eccentric 

Detail  Construction  ... 

"Slip"   . 

Open  and  Crossed  Rods     .  

Relation  Between  the  Center-Lines  of  Valve-Gear  and  Engine  Cylinder 

Design  of  a  Stephenson  Gear        .  

To  Find  Mid-Gear  Travel .        .  . 

To  Find  the  Lap  of  the  Valve 

To  Find  Position  of  Center  of  Saddle-Pin  for  Equalized  Cut-Off  at  Half  Stroke 
To  Locate  Bell-Crank  or  Tumbling-Shaft  for  Equalized  Cut-Off  at  All  Points  of  Stroke 
To  Find  the  Lead  on  the  Forward  and  Return  Strokes  in  Full-Gear        .... 
To  Find  Extreme  Travel  of  Link,  and  the  Slip 

-  Use  of  Models  in  Construction  of  Valve-Gears .        . 

Links 

Classifications  and  Types . 

Shifting  and  Stationary  Links 

Forms  of  Links  in  General  Use 

Drafting  Table  Problem,  No.  7. — Comparison  of  Results  from  Open  and  Crossed  Rods   . 

Types  of -Valve-Gears .  .100 

Gooch  Gear  ...  ...  .100 

Allen  Gear ....     100 

Fink  Gear     .  .     101 

Porter-Allen  Gear       .  .  -  .     102 

Walschaert  Gear 104 

Radial  Valve-Gears     .  .  .  .104 

Hackworth  Gear 105 

Marshall  Gear     ...  ...  .  .....     106 

Joy  Gear .107 

Baker  Gear  .  •  109 


viii  CONTENTS 

PAGE 

SECTION  V. — VALVE-GEARS — (Continued) 

Stevens  Gear       ....  110 

Lentz  Gear  .        .  .113 

Floating  or  Self-Centering  Valve-Gears  .  .     114 

Drafting  Table  Problem,  No.  8  ,.     116 

Steering  Gear       .        .  ..116 

Steam  Turbine  Gears     .  119 

Curtis  Steam  Turbine  Valve-Gear   .                        .  .                .                       .119 

• 

Westinghouse  Turbine  Valve-Gear 


VALVES,  VALVE=QEARS  AND  VALVE  DIAGRAMS 

SECTION   L— SIMPLE   STEAM-ENGINE. 

The  subject  of  valves  and  valve-gears  embraces  all  the  mechanism  of  a  steam-engine  which  is 
employed  in  automatically  regulating  the  admission  and  exhaust  of  steam  to  and  from  an  engine 
cylinder. 

ELEMENTS  OF  VALVES  AND  VALVE-GEARS. 

Names  of  Engine  Parts. 

The  elementary  parts  of  a  steam-engine  are  diagrammatically  shown  in  Fig.  1,  as  follows: 
A,  A'  is  the  engine  cylinder,  B  the  piston,  C  the  valve,  D  the  piston-rod,  E  the  connecting-rod, 
F  the  crank,  G  the  main-  or  crank-shaft,  H  the  eccentric-sheave,  J  the  eccentric-strap,  L  the  eccen- 
tric-rod, and  K  the  valve  stem. 

Point  e  is  the  pin  of  the  cross-head  which  travels  back  and  forth  between  two  straight  guides 
not  shown;  d  is  the  crank-pin;  a  is  the  center  of  a  circular  disc  called  the  "eccentric-sheave, "  which 
is  keyed  to  the  shaft;  b  a  is  the  eccentric  radius  and  is  equal  to  ]/^  the  travel  of  the  valve,  the  dotted 
circle  being  the  path  of  the  point  a,  g  the  "bridge-wall,"  and  h  the  "valve-seat." 

Crank  End,  Head  End,  Forward  Stroke,  Return  Stroke,  Dead-Center. 

Before  explaining  the  operation  of  the.  engine  some  of  the  terms  and  expressions  will  be  pointed 
out: 

The  "crank  end"  of  a  cylinder  is  the  end  nearest  the  crank  shaft.  The  "head  end"  is  the  end 
farthest  from  the  crank  shaft.  The  "forward  stroke "  of  an  engine  occurs  while  the  piston  is  moving 
toward  the  crank  shaft;  the  "return  stroke"  while  moving  away  from  it.  The  engine  is  said  to  be 
on  "dead-center"  when  the  crank,  connecting-rod  and  piston-rod  are  all  in  the  one  straight  line,  as 
shown  in  Fig.  1 .  There  are  two  dead-center  positions  in  each  cycle,  one  being  shown  in  Fig.  1  and 
the  other  occurring  when  the  crank  has  turned  180°  from  the  position  shown.  No  amount  of  steam 
pressure  on  the-  piston  will  turn  the  engine  when  it  is  on  either  dead-center. 

"Running  Over,"  "'Running  Under." 

When  referring  to  the  direction  of  rotation  of  an  engine  it  is  customary  to  speak  of  it  as  "run- 
ning over "  or  "running  under,"  instead  of  running  clockwise  or  counterclockwise.  The  latter  terms 
are  often  confusing  especially  in  an  engine  which  will  be  running  clockwise  to  a  person  standing 
on  one  side  and  counterclockwise  to  a  person  standing  on  the  other  side. 

An  engine  is  said  to  be  "running  over"  when  the  crank  rises  at  the  beginning  of  the  forward 
stroke,  or,  when  the  top  of  the  flywheel  turns  away  from  the  cylinder.  It  is  "running  under" 
when  the  crank  falls  at  the  beginning  of  the  forward  stroke,  or,  when  the  top  of  the  flywheel  turns 
toward  the  cylinder.  Stationary  engines  are  usually  designed  to  run  over,  while  locomotives 
must  necessarily  run  under,  the  cylinders  being  forward.  With  engines  running  over,  the  pressure 
between  the  crosshead  and  crosshead  guide,  due  to  the  angularity  of  the  connecting  rod,  comes  on 
the  lower  side  of  the  crosshead  only  and  on  the  body  of  the  engine  frame  directly;  whereas  in  engines 
running  under,  the  side  pressure  due  to  transmission  must  come  on  a  specially  designed  guide-part 
of  the  engine  frame  with  the  pressure  upward  away  from  the  main  body  of  the  frame. 

1 


VALVES,   VALVE-GEARS  AND   VALVE  DIAGRAMS 


Operation  of  Steam-Engine. 

In  the  working  of  a  steam-engine  the  parts 
operate  as  follows :  Steam  enters  the  steam-chest, 
Z  through  the  pipe  Y,  Fig.  1.  The  valve  C  is 
moved  (downward,  for  example),  and  the  steam 
passes  through  the  steam-port  W  to  the  cylinder 
A,  thus  driving  the  piston  B  to  the  opposite  end 
of  the  cylinder,  and  the  crank  F  and  the  eccentric 
center  a,  each  through  180°  to  the  positions  shown 
by  the  dotted  lines  F'  and  6  a'.  During  this 
period  of  motion  in  the  direction  of  the  arrow,  the 
valve  has  been  at  the  extreme  downward  position ; 
it  is  again  central,  and  is  moving  upward,  and  just 
admitting  steam  through  the  steam-port  W  to  the 
under  side  of  the  piston  which  is  now  at  the  bot- 
tom of  the  cylinder  A'.  At  the  same  instant  the 
steam-port  W  is  opened  to  the  exhaust-port  V,  and 
the  exhaust  steam  on  the  upper  side  of  the  piston 
escapes  through  the  exhaust  pipe  T. 

Observe  carefully  that  in  order  to  run  the  en- 
gine with  this  valve  the  effective  eccentric-arm  a  b 
must  be  set  at  90°  with  the  crank  F.  The  stu- 
dent cannot  hope  to  master  this  subject  without 
understanding  this  point  thoroughly,  and  always 
keeping  it  in  mind. 

Elementary  Steam  Valve. 

The  valve  C,  Fig.  1,  is  of  the  most  elementary 
form  (i.e.,  the  width  of  valve  at  seat  just  equals 
the  width  of  port),  and  a  study  of  the  figure  will 
show  that  it  admits  steam  during  the  entire 
stroke.  Such  a  valve  would  be  extremely  waste- 
ful, for  it  makes  no  use  of  the  expansive  power  of 
steam.  In  nearly  all  engines  this  elementary 
valve  is  modified  so  as  to  cut  off  the  admission  of 
steam  after  the  piston  has  been  forced  through 
only  a  part  of  the  stroke.  The  piston  is  then 
driven  through  the  remainder  of  the  stroke  by  the 
expansive  power  of  the  steam. 

Steam-Lap  and  Lap  Angle. 

The  modification  of  the  elementary  valve 
necessary  to  give  cut-off  at  a  fraction  of  the 
stroke,  consists  of  an  addition  known  as  the 
"steam-lap. "  In  Fig.  2  let  the  dotted  line  I  limit 
the  edge  of  the  elementary  valve;  then  I  m  is  the 


FIG 


steam-lap.  As  in  Fig.  1  the  engine  is  on  dead- 
center,  and  the  slightest  movement  of  the  valve 
downward  will  admit  steam  and  drive  the  piston, 
assuming  of  course  that  the  engine  has  sufficient 
momentum  to  pass  dead-center;  but  the  valve 
itself,  in  Fig.  2,  is  not  central  (with  respect  to  the 
steam-ports)  for  the  dead-center  position  of  the 
engine.  When  the  lap  I  m  was  added,  the  eccen- 
tric-sheave was  unkeyed  and  the  effective  eccen- 
tric-arm moved  from  6  a  to  bk  (while  the  crank  F 
remained  stationary),  so  as  to  make  the  distance 
c  d  equal  to  the  lap  I  m.  The  angle  a  b  k  is  called 
the  "lap  angle." 

Lead,  Lead  Angle,  Angle  of  Advance. 

In  Fig.  2  the  valve  is  set  so  as  to  admit  exactly 
at  the  end  of  the  stroke.  In  practice,  steam  is 
usually  admitted  to  the  cylinder  just  before  the 
end  of  the  stroke.  If  now  the  eccentric  is  turned 
still  further  (from  6  k  to  6  e)  while  the  engine  re- 
mains on  dead-center,  the  edge  m  of  the  valve  will 
be  drawn  a  small  distance  (equal  to  /  c)  across  the 
port  W.  This  distance  is  called  "lead, ''  and  in 
small  engines  is  about  %  inch.  The  angle  through 
which  the  eccentric  is  thus  turned  (angle  k  b  e)  is 
the  "lead  angle."  The  lap  angle  plus  the  lead 
angle  equals  the  "angle  of  advance"  (a  b  e).  The 
total  angle  by  which  the  eccentric  precedes  the 
crank  in  simple  cases  equals  90°  plus  the  angle  of 
advance.  This  entire  angle  is  termed  by  some  as 
the  "angle  of -advance,"  to  the  confusion  of  the 
subject  unfortunately.  The  majority,  however, 
define  angle  of  advance  as  given  above,  and  as  so 
defined  is  more  convenient  in  the  use  of  valve 
diagrams  and  the  study  of  the  subject  generally.  ' 

When  the  eccentric  center  is  at  k,  Fig.  2,  and 
turning  in  the  direction  of  the  arrow,  the  edge  m ' 
of  the  valve  is  moving  downward,  and  admission 
of  steam  to  the  cylinder  begins,  assuming  zero 
lead.  When  the  eccentric  center  is  at  A;'  (<n  b 
k'  =  <  a  b  k)  the  edge  of  the  valve  is  again  over 
the  edge  of  the  port  W,  but  is  now  moving  upward, 
and  admission  ceases.  Admission,  therefore,  has 
taken  place  while  the  eccentric  and  main  shaft 
have  turned  through  the  angle, 

k  b  k'  =  180°  -  2  a  b  k  .      .      .N     .      .    (1) 


FIG.  2. — Showing  valve  with  steam-lap  and  eccentric 
set  with  lap  angle. 


4  VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 

The  half  valve  travel  h  b  =  steam-lap  (c  d  =  b  g)  +  steam-port  opening  (h  g) .  Considering 
for  the  moment  a  zero  lead,  it  will  be  seen  that  the  greater  the  lap,  (I  m  =  c  d  =  b  g),  the  greater 
will  be  the  angle  of  advance  (abk),  and  the  smaller  will  be  the  angle  kbk'  and  the  steam-port  opening 
(h  g).  There  is  then  a  relation  between  the  steam-port  opening  and  the  lap  which  is  useful  in  the 
solution  of  later  problems.  For  example:  what  would  be  the  amount  of  lap  necessary  to  give  K 
cut-off,  assuming  zero  lead  and  the  connecting-rod  to  be  infinite  in  length? 

First,  the  crank  and  eccentric  will  each  have  turned  through  90°  when  cut-off  takes  place,  and 
the  angle  kbk'  will  be  90°,  leaving  the  angle  a  bk  =  45°  according  to  formula  (1)  on  page  1. 
Therefore,  c  d  =  b  g  =  sine  45°  =  0.707  and  h  g  —  0.293;  or,  the  ratio  of  lap  to  port  opening  for 

cut-off  under  these  conditions  is    ' 


Exhaust  lap 


Crank 
end 


Head 


[  FIG.  3. 

Exhaust-Lap. 

In  these  notes  the  steam-  or  outside  lap  has  already  been  referred  to,  and  shown  in  Fig.  2.  Most 
valves  have  also  " exhaust"  or  " inside  lap,"  which  is  formed  by  adding  metal  to  the  inside  of  the 
valve  so  as  to  cover  a  small  part  of  the  bridge  when  the  valve  is  central.  See  Fig.  3  in  which  the 
exhaust-lap  is  E  D.  The  use  of  the  exhaust-lap  will  appear  later. 

Finite  and  "Infinite"  Connecting- Rods— Effect  of  Angularity  in  the  Finite  Rod. 
In  all  practical  valve  work  the  effect  of  the  changing  angles  of  the  finite  connecting-rod  during 
each  revolution  of  the  crank  must  be  taken  into  account.     Starting  from  dead-center  position, 
head  end,  it  is  quite  evident  that  when  the  piston  is  half-way  through  its  stroke  the  crank  cannot 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  5 

be  exactly  90°  advanced;  on  the  forward  stroke  it  will  be  less  than  90°,  see  angle  a  Fig.  4  and  on  the 
return  stroke  more  than  90°,  see  angle  r.  It  will  be  exactly  90°  with  the  "infinite"  connecting- 
rod,  for  whfch  there  is  a  mechanical  equivalent,  (see  Fig.  5),  which,  however,  is  seldom  used.  The 
motion  o7  the  point  /  in  the  "infinite"  connecting-rod,  Fig.  5,  is  harmonic,  or  exactly  equivalent 
to  thatfbf  the  point  c  which  is  the  projection  of  b;  whereas  in  Fig.  6,  the  point  /  moves  faster  than 
c  wliile  b  is  moving  from  d  to  I,  and  slower  while  6  is  moving  from  I  to  m. 

The  length  of  the  connecting-rod  varies  in  practice  from  4  to  8  times  the  length  of  the  crank 
fbt -steam-engine  work.  In  this  course  it  will  always  be  taken  as  5  times,  unless  otherwise  specified. 

The  effect  of  the  angularity  of  the  eccentric-rod  is  generally  so  very  small  that  it  is  inappreciable, 
and  is  therefore  neglected.  This  becomes  evident  when  it  is  considered  that  the  length  of  the 
eccentric-rod  is  20  to  30  times  the  eccentric  radius. 

In  the  work  of  valve  design  it  is  necessary  to  adopt  some  graphical  method  which  will  show  at 


FIG.  4.  , 

a  glance  the  steam  distribution  at  any  instant,  and  also  the  several  positions  of  the  crank  at  the 
points  of  admission,  cut-off,  release  and  compression. 

In  Fig.  2  the  valve  is  shown  in  position  for  admission,  considering  that  it  is  moving  downward. 
After  traveling  to  its  lowest  point  and  returning  to  the  position  illustrated,  cut-off  of  the  steam  takes 
place  and  expansion  occurs.  As  the  valve  continues  to  move  upward,  P  reaches  q,  when  release 
takes  place,  the  steam  exhausting  into  the  exhaust  port  T.  The  valve  then  continues  to  its  highest 
position,  and  when  P  reaches  q  on  the  return  the  steam  in  the  cylinder  is  trapped  for  a  very  short 
time,  during  which  the  piston  continues  to  move  upward  and  compression  takes  place. 

ZEUNEK  DIAGRAM. 

Several  methods  have  been  devised  to  show  graphically  the  relative  positions  of  the  valve  and 
crank,  and  the  steam  distribution,  and  while  each  of  the  more  common  methods  will  be  briefly 
described  later  on,  the  one  to  be  used  in  this  course  will  now  be  taken  up.  It  is  known  as  the  "  Zeuner 
diagram."  This  diagram  shows  how  far  the  valve  is  from  its  central  position  for  any  position  of 
the  crank.  Knowing  then  the  dimensions  of  the  valve  and  the  valve-seat,  the  actual  opening  of 
the  port  for  any  crank  position,  either  for  entering  or  exhaust  steam,  is  seen  at  a  glance. 


6  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

In  Fig.  7  let  A  B  represent  any  position  of  the  crank.  Then  if  an  angle  of  advance  of  30°  be 
assigned,  the  eccentric  will  be  120°  in  advance  of  the  crank,  or  in  the  position  A  C. 

When  it  is  in  the  position  A  C,  Fig.  7,  the  valve  must  be  off  center  a  distance  C  L  =  A  D.  But 
A  D  =  A  E  since  the  diameter  of  the  circle  A  E  F  equals  the  radius  of  the  eccentric  circle,  and 
the  right-angle  triangles  A  E  F  and  A  D  C  are  equal. 

The  radial  distance  A  E  then  represents  the  amount  the  valve  is  off  center,  and  if  there  were 


FIG.  5. 


no  lap,  as  in  Fig.  1,  it  would  be  the  amount  of  port  opening  with  the  crank  at  A  B.     (Fig.  7  it  will, 
be  understood,  is  on  a  much  larger  scale  than  Fig.  1). 

Remembering  that  the  eccentric  is  120°  in  advance  of  the  crank,  A  C,  together  with  the  circle 
A  E  F,  may  be  turned  back  this  amount,  when  A  C  will  coincide  with  A  B,  and  E  will  fall  at  G  and 
the  circle  A  E  F  at  A  G  H.  The  angle  F  A  H ,  then,  is  120°,  and  taking  from  it  the  right-angle 
F  A  K  there  is  left  K  A  H  =  30°,  which  is  the  angle  of  advance.  A  G,  on  the  crank-line  position, 
now  measures  the  amount  the  valve  is  off  center  for  that  crank  position,  The  circle  A  G  H  when 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  7 

laid  off  with  the  proper  angle  of  advance,  may  be  called  specifically  the  "Zeuner  circle,"  for,  no 
matter  where  the  crank  position  is  drawn,  the  part  lying  within  this  circle  always  measures  the 
amount  the  valve  is  off  center. 

That  A  G  is  equal  to  C  L,  Fig  7,  and  therefore  shows  the  amount  the  valve  is  off  center  may 
also  be  shown  briefly  as  follows: 

<  N  A  K  =  <  M  A  B,  lines  respectively  perpendicular 

<  C  A  N  =  <  K  A  H,  by  construction 

/.90°—  ,«NAK  +  <  CA  N)  =  90°  —  (<  M  AB  +  <  K  A  H)  and  <CAF  =  <HAB 
.' .  ^  A  C  D  and  A  H  G  are  right  triangles  having  equal  angles  at  their  vertices  and  equal  sides 
A  C  and  A  H.     They  are  therefore  equal  and  AG  =  AD  =  CL.     Q.  E.  D. 


FIG.  7.— Showing  Development  of  Zeuner  Diagram. 

In  using  the  Zeuner  diagram  it  must  be  kept  constantly  in  mind  that  the  angle  of  advance  is 
laid  off  in  the  opposite  direction  from  that  in  which  the  engine  is  turning  when  the  eccentric  is 
directly  connected  to  the  valve-stem. 

Application  of  the  Zeuner  Diagram. 

Fig.  8  is  a  practical  application  of  the  Zeuner  diagram  showing  the  events  for  the  head  end 
steam-port.  The  throw  of  the  eccentric,  the  angle  of  advance,  and  the  steam  and  exhaust  laps 
are  assumed.  A  K  =  %  the  travel  of  the  valve.  K  A  H  =  the  angle  of  advance.  When  the 
crank  is  afcAJV_the  valve  is  off  centftrjhhe  distance  A^J).  But  A  D  equals  the  steam-lap^  or  the^ 
distance  the  valve  has  to  t'faTeTfrom  its  central  position  before  it  begins  to  open  the  steam-port. 


8  ST  VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 

jf^ ' 

\S  Therefore  the  Zeuner  diagram  shows  that  steam  bejgins  to  enter _toe.  _ cylinder  jffihen  the  crank  is  at 
~ArN :  At  the  end  pftn^sTroke^Qr  on  thejiead-center  position,  when  the  crank  is  at  A  C,  the  valve 
is  off  center  the  distance  A  B,  and  the  steam-port  is  open  the  amount  of  the  lead  =  E  B.  With  the 
crank  at  A  H  the  valve  is  at  its  extreme  left-hand  position,  and  the  steam-port  is  open  the  maximum 
amount  equal  to  F  H.  When  the  crank  arrives  at  A  V  P  the  steam-port  opening  is  zero,  and  cut- 
off takes  place.  Steam  has  been  admitted  then  while  the  crank  has  been  turning  from  A  N  to  A  P. 
When  the  crank  reaches  A  T  (tangent  to  the  Zeuner  circles)  the  valve  is  central,  and  if  there 


FIG.  8. — Application  of  the  Zeuner  Diagram  to  the  Events  of  the  Head  End  Steam  Port. 

were  no  exhaust-lap,  exhaust  would  begin.  But  in  Fig.  8  an  exhaust-lap  equal  to  A  L  has  been 
assumed;  the  valve  must  therefore  move  the  distance  A  L  or  A  J,  and  the  crank  reach  the  position 
A  J  Q  before  exhaust  begins.  The  exhaust  opening  continues  to  increase  until  it  reaches  its  maxi- 
mum, L  R,  at  A  R,  and  then  decreases  until  it  closes  altogether  at  A  S.^  The  unexhausted  steam 
at  that  instant  is  then  trapped  in  the  cylinder,  and  as  the  piston  nears  the  end  of  the  return  stroke, 
the  steam  must  be  compressed  until  the  crank  reaches  A  N,  when  admission  again  takes  place, 
and  the  cycle  is  completed. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


9 


The  Zeuner  diagram  showing  the  events  for  the  crank  end  port  may  have  the  steam-lap  arc 
D  F  V  continued  to  intersect  the  circle  A  J  R  M ,  and  the  exhaust-lap  arc  J  L  M  continued  to  inter- 
sect the  circle  A  D  H  V;  and  crank  end  admission  would  begin  just  before  the  crank  reached  A  0, 

Principal  Phases  of  a  Steam-Engine  Cycle. 

The  four  principal  phases  of  the  stroke  are  called  "Admission  (.A  N),  "Cut-off"  (A  P),  "Re- 
lease" (A  Q),  and  "Exhaust  Closure"  (AS). 

Observe,  and  commit  to  memory  the  fact  that  \  steam  or  I    jap  controls  admission  and  cut-off, 

(  outside  j 

and  that  exhaust-lap  controls  release  and  exhaust  closure.    . 


CRANK 


Positive  and  Negative  Exhaust-Laps. 

The  exhaust-lap  shown  by  A  J  in  Fig.  8  is  termed  positive  exhaust-lap  because  it  represents 
metal  added  to  the  elementary  valve,  and  because  the  valve  has  to  travel  an  additional  amount 
beyond  its  central  position  to  open  the  port  to  exhaust  steam.  But  it  frequently  happens,  in  order 
to  obtain  a  more  desirable  steam  distribution  to  fit  special  conditions,that  the  exhaust-lap  is  decreased 
in  which  case  it  may  be  zero  when  the  arc  J  M  would  reduce  to  the  point  A,  the  valve  would  open 


10 


VALVES,   VALVE-GEARS  AND   VALVE  DIAGRAMS 


to  exhaust  just  as  it  reached  its  central  position,  and  A  R  would  be  the  maximum  exhaust-port 
opening;  or,  the  exhaust  lap  may  be  negative,  in  which  case  it  represents  metal  cut  away  from  the 
inside  edge  of  the  elementary  valve,  and  the  valve  opens  the  port  to  exhaust  before  it  reaches  its 
central  position  as  shown  in  Fig.  9. 

The  negative  exhaust  lap  in  Fig.  9  is  A  L;  exhaust  begins  when  the  crank  is  at  A  Q  and  the  valve 
is  on  center  when  the  crank  is  at  A  T.  The  maximum  port  opening  to  exhaust  would  be  R  A  +  A  L 
providing  the  steam-port  were  that  wide.  When  the  distance  R  L  becomes  greater  than  the  steam- 
port  width  the  engine  is  said  to  have  "full  exhaust  opening."  The  intercept  on  the  dead-center 
crank  position  A  0  between  the  exhaust  lap  and  Zeuner  circles,  W  G  in  Fig.  9,  is  sometimes  called 
the  "exhaust  lead."  A  valve  having  negative  exhaust  lap  equal  to  A  L,  Fig.  9,  is  illustrated  in 
Fig.  10,  to  1A  size,  both  figures  having  corresponding  letters  where  possible.  The  negative  exhaust 
lap  is  shown  at  A  L. 

Exercise  Drills  in  the  Use  of  the  Zeuner  Diagram. 

A  valve  diagram  is  of  such  great  importance  in  analyzing  steam  distribution  for  a  valve,  that  it 
should  be  thoroughly  understood  at  the  start.  In  order  to  acquire  such  understanding  the  student 


HEAD 
END 


HEAD 
END 


Fig.  14 


should  follow  the  exercises,  problems  Nos.  1, 2  and  3,  which  are  explained  on  succeeding  pages,  and 
also  .construct  for  himself  the  original  problems  numbered  4,  5  and  6.  To  facilitate  the-  drawing 
of  the  Zeuner  diagram  it  is  customary  to  arrange  it  so  that  the  live  steam-lap,  head  end,  falls  in  one 
of  the  upper  quadrants,  usually  the  right-hand  quadrant,  regardless  of  the  other  items  in  the  data. 
This  arrangement  of  the  diagram  will  always  give  the  correct  result  in  showing  how  much  the  valve 
is  off  center,  and  the  port  opening,  for  a  given  crank  position;  also  the  relative  positions  of  the  crank 
at  admission,  cut-off,  release  and  compression,  but  it  will  not  show  these  relative  positions  of  the 
crank  in  their  right  places  with  reference  to  the  engine  base  and  cylinder.  This  is  illustrated  in 
Figs.  11,  12,  13  and  14,  where  it  will  be  seen  that  for  the  crosshead  position  T,  which  is  about  .08  on 
the  forward  stroke,  in  each  case,  that  the  valve  is  off  center  a  distance  A  X  and  the  port  open  an 
amount  W  X,  and  these  values  are  equal  in  all  four  figures.  Also  the  crank  positions  for  all  events 
are  the  same  distances  from  each  other  in  all  four  figures.  When  the  data  specify  only  crank 
positions  it  is  not  necessary  to  draw  the  crosshead  position  and  the  diagram  may  be  arranged  as 
in  Fig.  11,  but  when  the  piston  positions  are  specified  it  is  more  satisfactory  to  arrange  the 
diagram  so  the  resultant  crank  positions  will  show  in  their  right  places  relatively  to  the  engine  frame. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


11 


1.  Given:  Eccentricity,  crank  position  at  cut-off,  angle  of  advance,  and  compression. 

Find:  Steam-lap,  exhaust-lap,  crank  positions  at  admission  and  release,  lead,  exhaust-lead,  and 
greatest  steam  and  exhaust  port  openings. 

The  solution  of  this  problem  is 
shown  in  Fig.  15,  the  data  being  in 
dash-line  construction,  and  the  rest  of 
the  work  in  solid-line  construction. 
The  order  of  drawing  all  the  lines  is 
shown  by  the  numerals  on  each.  The 
steam-lap  is  o  g;  exhaust-lap,  o  t;  crank 
position  at  admission,  o  r,  and  at  release 
o  q;  lead,  h  k;  exhaust  lead,  m  n;  great- 
est steam  opening,  s  c;  greatest  exhaust 
port  opening  t  d. 

2.  Given:  Steam-lap,  lead,  crank 
position  at  cut-off,  and  exhaust-lead.  | 

Find:  Valve-travel,  angle  of  ad- 
vance, exhaust-lap,  and  crank  positions 
at  admission,  release  and  compression. 

The  data  are  given  in  Fig.  16  in 
dash  lines  and  by  the  distances  6  c  and 
g  h.  The  results  are:  e  d  —  valve- 
travel;  m  o  d  =  angle  of  advance; 
o  k  =  exhaust-lap  ;of,ok  and  o  I  =  crank 
positions  at  admission,  release  and 
compression  respectively. 

3.  Given :  Cut-off,  lead,  and  steam- 
port  opening. 

Find:  Lap,  valve-travel,  and  angle 
of  advance. 

In  Fig.  17,  draw  given  crank  cut-off 
position  o  t,  and  on.  o  t  extended  lay  off 
o  a  =  lead  to  enlarged  scale.  Make 
ab  =  given  steam  opening  to  same  en- 
larged scale.  Then  draw  b  u  parallel 
to  line  of  stroke,  and  make  be  =  b  a. 
Draw  o  c  and  on  it  lay  off  o  d  =  o  a, 
and  draw  horizontal  line  d  /.  With 
radius  o  e  (where  u  b  crosses  vertical 
center  line)  draw  circular  arc  e  v,  and 
lay  off  arc/  h  =  arc  g  e.  Draw  line  h  w, 
which  will  contain  the  diameter  of  the 
Zeuner  circle  and  y  o  w  will  be  the 
angle  of  advance.  Take  any  point  as  j 
as  center  for  a  trial  Zeuner  circle.  This 
gives  a  port  opening  of  z  k,  and  lead  of  FIG.  16. 


FIG.  15. 


m 


\ 


\ 


12 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


I  m,  which  are  too  small  each  in  the  same  proportion.  Since  z  k  is  the  trial  port-opening  and 
a  b  the  desired  opening,  draw  k  q  in  any  direction,  lay  off  k  n  =  a  b,  draw  z  n,  and  o  i  parallel  to 
z  n.  Then  in  =  radius  of  desired  lap  circle,  and  k  i  =  w  o  =  diameter  of  the  Zeuner  circle  or  Yi 
valve  travel,  p  x  =  lead  =  o  a.  The  proof  for  this  construction  is  given  in  Spangler's  "Valve 
Gears, "p.  22. 

The  data  for  this  problem  are  those  usually  assigned  in  practical  work.  The  involved  graphical 
solution  here  given  is  not  easily  remembered  and  therefore  not  generally  used,  the  simple  method 
given  in  connection  with  drafting-table  problem  No.  1,  p.  17,  being  the  one  usually  employed  since 


FIG.  17. 


it  may  be  developed  from  elementary  knowledge  without  reference  to  any  book  or  notes.     An 
analytical  solution  by  Mr.  G.  A.  Pfeiffer,  M.E.,  (Stevens  '10)  using  the  formula, 


Steam-lap  = 


26  -a 


where  a  =  lead,  b  =  steam-port  opening,  both  in  inches,  and  d  —  cosine  of  angle  measured  between 
dead-center  and  cut-off  crank  positions,  may  also  be  used.  It  is  of  special  advantage  in  cases  where 
the  lead  is  large  relatively  to  port-opening, 

Exercise  Problems. 

4.  Given:  Valve-travel,  steam-lap,  zero  lead,  and  negative  exhaust-lap. 

Find:   Angle  of  advance,  crank  positions  at  admission,  cut-off,  release  and  compression,  also 
maximum  steam  and  exhaust-port  openings. 

5.  Given:  Crank  positions  for  admission  and  cut-off  on  head  end,  and  for  admission  on  crank 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


13 


end;   also,  valve-travel,  and  positive  exhaust-lap  on  head  end,  and  negative  exhaust-lap  on  crank 

end. 

Find  :  Steam-lap  for  both  ends,  crank  positions  at  release  and  compression  for  both  ends,  cut-off 

crank  end,  lead  for  both  ends. 

6.     Given:  Angle  of  advance,  valve-travel,  negative  lead,  and  crank  position  at  compression. 
Find.  Steam-  and  exhaust-laps,  and  crank  positions  at  admission,  cut-off  and  release. 

STEAM-PIPES,  STEAM-PORTS  AND  STEAM-PORT  OPENING. 

The  areas  of  the  steam-pipes,  ports  and  port-openings  dep3nd  on  the  size  of  the  cylinder  and  the 
speed  of  the  piston. 
Let  L  be  the  length  of  the  piston  stroke,  in  feet, 

D  the  diameter  of  the  cylinder,  in  inches,  and 

N  the  number  of  revolutions  per  minute. 

r-\2 

Then  the  volume  swept  through  by  the  piston  per  minute  will  be  represented  by  2  N  L  —  —  .  The 

velocity  V  (infect  per  min.)  of  the  steam  through  the  port-opening,  multiplied  by  the  area  A  (in  sq. 
ins.)  must  be  equal  to  the  above  expression,  thus  giving  the  equation 


Distinction  Between  Port  Width  and  Port  Opening. 

Good  average  practice  in  a  large  number  of  engines  allows  a  velocity  of  6,000  to  8,000  feet  per 
minute  for  the  supply  steam-pipe,  and  for  the  steam-port  opening.  A  velocity  of  4,000  to  6,000  feet 
per  minute  is  allowed  for  the  exhaust  through  the  steam-port.  The  distinction  between  "steam- 
port"  and  "steam-port  opening"  should  be  carefully  noted.  It  is  as  follows: 

Since  only  one  port  leads  to  one  end  of  the  cylinder  in  the  simple  engine,  it  is  evident  that  the 
supply  or  live  steam  must  go  in,  and  the  exhaust  steam  come  out  of  the  same  port.  The  allowance 
usually  made  for  the  velocity  of  the  exhaust  steam  regulates  the  area  of  the  steam-port  which  must 
be  entirely  uncovered  by  a  sufficient  travel  of  the  valve  when  opening  to  the  exhaust  port.  When  the 
valve  opens  the  steam-port  for  the  admission  of  live  steam, 
it  is  evident  that  the  entire  area  of  the  steam-port  need 
not  be  uncovered,  on  account  of  the  live  steam  flowing  at 
a  faster  rate  than  the  exhaust.  The  amount  that  is  un- 
covered is  called  the  "  steam-port  opening.  "  This  opening 
is  usually  less  than  the  width  of  the  port,  but  in  some  engines 
other  considerations  control  the  design,  and  the  edge  of  the 
steam-lap  of  the  valve  may  not  only  cross  the  entire  width 
of  the  port,  but  also  traverse  a  small  part  of  the  bridge. 

Overtravel 

The  amount  that  the  cut-off  edge  of  the  valve  travels 
beyond  the  live-steam  edge  of  the  bridge  is  termed  by  some 
as  "overtravel";  whereas  it  appears  more  logical  to  term 
that  travel  of  the  valve  beyond  the  point  necessary  to  give 
the  full  calculated  steam-port  opening  as  the  overtravel, 
and  this  word  will  be  used  in  the  latter  sense  throughout 

this  book.     As  an  illustration,  refer  to  the  Zeuner  diagram,  Fig.   18.     There  it  will  be  assumed 
that  it  has  been  expedient  to  make  the  half-valve  travel  equal  to  a  r,  whereas  the  calculated  steam- 


U 


14  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

port  opening  turns  out  to  be  t  1;  I  r,  then,  becomes  the  overtravel.  This  overtravel  would  be 
represented  on  the  valve  seat  itself  by  the  amount  A  travels  beyond  C  in  Fig.  3,  p.  4.  In  an 
engine  already  built  the  point  C,  of  course,  would  not  be  in  evidence,  but  in  order  to  take  intelligent 
action  with  respect  to  the  valve  or  valve-gear,  it  would  be  necessary  to  make  computations  as  to 
port-opening,  etc.,  thus  locating  C  after  which  the  overtravel  could  be  readily  determined.  If  the 
overtravel  should  be  great  enough  to  come  too  close  to  the  exhaust  side  of  the  bridge  alterations 
must  be  made  either  in  the  valve-travel  or  the  bridge  thickness;  this  case  will  be  taken  up  in  con- 
nection with  drafting-table  problem  No.  1,  p.  17. 

Formula  for  Calculating  Live  and  Exhaust  Steam-Ports. 

T\2  I Y* 

In  writing  the  formula  V  A  =  2  N  L—  -  the  symbol  a  is  usually  substituted  for  —  — ,  and  A  and 
a  are  expressed  in  square  inches,  while  L  and  V  are  given  in  feet.  The  equation  should  then  be 
written  12  V  A  =  2  X  12  L  a  N,  or  cancelling  and  transposing,  A  =  — ^ . 

Actual  and  Average  Velocity  of  Flow  of  Steam  Through  'Ports. 

In  building  up  this  formula,  it  will  be  observed  that  the  quantity  of  steam  per  minute  was  based  on 
an  assumption  that  steam  entered  the  cylinder  during  the  entire  stroke.  Inasmuch  as  engines  cut 
off  anywhere  from  }4:to%  stroke,  as  a  rule,  this  may  seem  a  needlessly  large  assumption;  but  it  must 
be  remembered  that  it  is  the  rate  at  which  steam  is  required  at  a  given  instant  that  counts,  and  not 
the  period  during  which  it  is  required.  Owing  to  the  varying  velocity  of  the  piston,  the  rate  of  flow 
of  6,000  ft.  per  minute  here  provided  is  only  an  average  rate,  and  means  nothing  so  far  as  actual 
rate  of  flow  through  the  ports  at  any  given  instant,  is  concerned.  It  is  purely  an  empirical  value 
based  on  practical  experience. 

To  find  the  actual  velocity  of  the  steam  through  the  ports  for  any  given  engine  or  any  given  de- 
sign, it  would  be  necessary  to  find  the  piston  velocity  and  the  port-opening  at  successive  intervals 
from  which  the  actual  rate  of  flow  through  the  port  at  these  phases  could  be  determined,  the  area  of 
the  piston  being  known.  If  these  values  were  plotted  as  ordinates,  a  curve  would  be  obtained  in 
which  the  maximum  ordinate  would  give  the  maximum  rate  of  flow  of  steam  through  the  ports. 

In  the  ordinary  engine  an  approximation  to  the  maximum  steam  velocity  through  the  ports  may 
be  obtained  by  considering  that  the  full  steam-port  opening  area  is  uncovered  at  the  instant  that  the 
piston  has  it  maximum  velocity.  The  maximum  piston  velocity  F,  is  equal,  approximately,  to  the 
crank-pin  velocity.  Therefore  the  approximate  maximum  steam  velocity  through  the  port  opening 
equals  1 

2  IT  R  N  x      *•  #2 


The  average  velocity  equals  , 

2LN  X-TT  D*  • 

v .          A* 

Therefore  the  ratio  of  approximate  maximum  velocity  to  the  average  velocity  ordinarily  used  in 
computations  for  engine  design  equals 

FA  —  f 

i  -fl  ~JLV 

vx __^_ 

'  A  _.  ,  ,T  v  f  1  L 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS  15 

But  since  L  =  2  R, 

Z>  _*     • 
V    ~  2 

The  average  steam  velocity,  F,  in  the  above  formula,  allowed  by  builders  of  different  types  and 
sizes  of  engines,  varies  widely,  and  instea*d  of  6,000  to  8,000  feet  per  minute,  10,000  and  even  more  is 
sometimes  used. 

After  the  area  of  the  port  has  been  calculated,  a  length  must  be  assumed  in  order  to  determine 
the  breadth.  In  plain  slide-valve  engines  the  length  of  the  port  varies  in  practice  from  Y%  to  %  of  the 

diameter  of  the  cylinder. 

NOTE  BOOK  PROBLEMS. 

The  problems  here  given  should  be  carefully  worked  out  in  a  large  note  book  or  on  large  pad 
paper.  They  are  preliminary  to  the  drafting-table  problems  which  follow. 

Prob.  1.  Construct  on  large  scale,  a  valve  and  valve-seat  with  assumed  values  for  the  live 
steam  and  exhaust  steam-laps,  the  bridge,  the  exhaust-port,  the  steam-ports,  the  steam-port  open- 
ing, and  the  half  valve-travel,  all  plainly  marked. 

Prob.  2.  Make  orthographic  drawing  on  enlarged  scale  of  the  lower  part  of  Fig.  2  of  this  book, 
assuming  the  angles  abk  and  k  b  e,  the  eccentric  center  at  e,  and  engine  on  dead-center.  In  deter- 
mining the  angle  made  by  the  center-line  of  eccentric-rod  with  the  center-line  of  the  engine,  the 
eccentric-rod  length  may  be  taken  equal  to  20  X  eccentric  radius.  Mark  plainly  by  use  of  reference 
letters : 

(1)  Lap  angle.  (3)  Angle  of  advance.  (5)  Lead. 

(2)  Lead  angle.  (4)  Steam-lap.  (6)  Port-opening. 
(7)  Half  valve-travel. 

(8)'  Angle  through  which  crank  turns  while  the  piston  is  moving  from  end  of  stroke  to  point  of 
cut-off. 

(9)  Angle  through  which  the  crank  turns  while  steam  is  being  admitted. 

Prob.  3.  Construct,  to  full  size  scale,  an  eccentric-sheave,  eccentric-strap,  and  part  of  eccentric- 
rod  that  will  give  a  2"  valve-travel  when  mounted  on  a  2j/£"  shaft. 

Prob.  4'  To  show  the  variable  motion  of  the  piston  during  forward  and  return  strokes  caused 
by  the  angularity  of  the  connecting-rod  when  the  center-line  of  the  stroke  passes  through  the  axis  of 
the  shaft. 

Draw  to  scale  a  crank,  a  connecting-rod,  and  the  cross-head  travel,  making  the  connecting-rod 
equal  to  4  crank  lengths.  Assume  the  crank  length. 

From  the  drawing,  fill  in  the  blank  spaces  in  the  following  items: — 

(1)  When  the  piston  is  at  3^  the  forward  stroke  the  crank  has  turned  through degrees 

approximately. 

(2)  When  the  piston  is  at  ^  the  return  stroke  the  crank  has  turned  through degrees 

approximately. 

(3)  When  the  crank  has  turned  through  90°  on  the  forward  stroke  the  piston  is  at %  of  its 

stroke  approximately. 

(4)  When  the  crank  has  turned  through  90°  on  the  return  stroke  the  piston  is  at ........%  of  its 

stroke  approximately. 

(5)  The  maximum  angle  of  the  connecting-rod  is degrees  approximately. 

Prob.  5.  To  show  the  variable  motion  of  the  piston  during  forward  and  return  strokes  caused  by 
the  angularity  of  the  connecting-rod  when  the  center-line  of  stroke  is  tangent  to  the  crank-pin  circle. 


16 


VALVES,  VALVE-GEARS  AND  VALVE   DIAGRAMS 


Make  drawing  to  scale  using  same  dimensions  for  crank  and  connecting-rod  as  in  Prob.  4,  and  fill 
in  the  blank  spaces  in  the  following  items: 

(1)  The  piston  travel  = X  crank  length. 

(2)  The  crank  travel  = degrees  approximately  .on  the  forward  stroke. 

(3)  The  crank  travel  = degrees  approximately  on  the  return  stroke. 

(4)  The  piston  pressure  is  transmitted  without  angularity  of  the  connecting-rod  and  with  maxi- 
mum crank  leverage  when  the  piston  is  at %  of  its  forward  stroke.     This,  together  with  the 

fact  that  the  angularity  of  the  rod  varies  from  a  minimum  to  a  maximum  of to 

degrees  during  the  return  stroke  makes  it  useful  only  for  single  acting  engines. 

Prob.  6.    Determine  the  ratio  of  lap  to  port-opening  for  0.7  cut-off  and  zero  lead; 

(1)  For  connecting-rod  =  5  crank  lengths, 

(2)  For  infinite  connecting-rod. 

In  drawing  make  separate  crank  and  eccentric  circles. 

Prob.  7.  Determine  the  ratio  of  lap  to  port-opening  for  0.4  cut-off  and  zero  lead,  for  a  connect- 
ing-rod equal  to  4  crank  lengths. 

Prob.  8.  Find  the  maximum  rate  of  flow  of  live  steam  through  the  port-opening  of  an  engine 
having  10"  bore,  18"  stroke  and  250  r.p.m.  in  which  the  port-opening  has  been  designed  for  an  aver- 
age rate  of  flow  of  live  steam  of  6,000  ft.  per  minute. 

Prob.  9.  Given:  valve-travel  =  3",  angle  of  advance  =  zero,  steam-lap  =  %",  exhaust-lap  = 
%",  steam-port  width  =  1^",  bridge  %",  and  exhaust  port  =  2^".  Find  the  crank  positions 
for  admission,  cut-off,  release,  and  compression.  Construct  the  valve-seat,  and  the  valve  in  its 
proper  position  for  the  beginning  of  the  stroke.  Indicate  the  maximum  steam-port  opening,  ex- 
haust-port opening  and  lead,  both  on  Zeuner  diagram  and  valve-seat.  Then  assume  any 'crank 
position  and  dot  the  corresponding  position  of  valve  on  the  valve-seat  and  mark  the  port-opening 
for  that  position  on  both  the  Zeuner  diagram  and  valve -seat. 

Prob.  10.  Let  the  data  and  requirements  be  the  same  as  the  previous  problem,  only  chang- 
ing the  angle  of  advance  to  30°.  Take  the  assumed  crank  position  in  the  same  place  as  in  Problem  9. 

Prob.  11.  Show  effect  of  changing  conditions  as  indicated  in  the  first  column  of  the  following 
table,  on  the  time  when  the  principal  events  of  the  stroke  occur,  based  on  a  study  of  Probs.  9  and  10. 
Fill  out  the  following  Table: 


Admission. 

Cut-off. 

Release. 

Exhaust  closure. 

Increase  in  Angle  of 
Advance. 

• 

Increase  in  Valve- 
Travel. 

Increase  in  Steam- 
Lap. 

Increase  in  Exhaust- 
Lap. 

VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


17 


DRAFTING  TABLE  PROBLEM,  No.  1. — PLAIN  D- VALVE. 

Design  a  slide-valve  for  an  engine  having,  ./.bore  and.  .'1.  stroke,  running  at'  ^'.revolutions  per 
minute.  Cut-off  at.  ..  .stroke  head  end;  release  at.  .  .stroke  both  ends;  lead r-£/. head  end; 
average  velocity  of  live  steam  through  ports  100  feet  per  second;  length  of  connecting-rod  4  times 
the  crank.1 


b.  per  second;  length  of  conncctmg-r 

<JU. 

Construction  of  Zeuner  Diagram. 


Calculate  the  area  of  the  port-opening  for  the  given  steam  velocity.  Make  the  length  of  the  port 
0.7  of  the  bore,  and  determine  the  width  of  the  port-opening. 

By  means  of  the  Zeuner  diagram  the  necessary  steam-lap,  exhaust-lap,  the  valve-travel  and  the 
angle  of  advance  may  be  found  as  follows: 


CRANK   END 


HEAD  EN 


m      r 


FIG.  19. 

On  the  horizontal  line  y  z,  Fig.  19,  set  off  a  o  equal  to  the  crank  length  ,  o  n  equal  the  length  of  the 
connecting-rod,  and  n  m  equal  to  the  stroke,  to  the  largest  scale  that  the  drawing  paper  will  accom- 
modate. In  doing  this  consider  m  n  the  cross-head  travel  instead  of  the  piston  travel,  o  p  y  is  then 
the  crank-pin  circle,  and  a  the  center  of  the  crank-shaft. 

Find  the  position  a  p  of  the  crank  for  the  assigned  cut-off.  A  trial  steam-lap  for  the  head  end  of 
the  valve  which  will  give  this  cut-off  approximately  should  then  be  found  by  means  of  the  relation 
existing  between  port-opening  and  steam-lap  as  explained  on  pp.  3  and  4  of  this  book. 

Inasmuch  as  a  definite  amount  of  lead  is  assigned  in  this  problem  the  ratio  of  lap  to  port-opening, 
just  referred  to,  will  not  be  exact  in  this  case.  It  will,  however,  be  approximately  correct,  and  will 
serve  as  a  guide  in  obtaining  the  exact  lap  as  follows:  At  the  intersection  of  the  trial  lap  circle,  a/, 
Fig.  19,  with  the  cut-off  crank  line  a  p,  draw  a  perpendicular  f  g.  From  b  where  the  trial  lap  circle  in- 
tersects the  engine  center-line,  lay  off  distance  6  c  equal  to  the  lead  on  the  scale  adopted  for  the  trial 
lap  circle.  At  c  erect  a  vertical  line  until  it  meets/ g.  Then  if  the  radial  distance  s  g  equals  the  cal- 

1  The  above  data  for  the  cut-off  and  release  refer  only  to  the  head  end  of  the  cylinder.  After  the  dimensions  for 
the  head  end  of  the  valve  have  been  found  according.to  the  following  directions,  instruction  regarding  the  crank  end 
will  be  given. 


18 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


culated  width  of  the  port-opening  according  to  the  adopted  scale,  the  assumed  lap  is  the  correct  one. 
It  is  not  to  be  supposed  that  one  will  assume  the  correct  lap  circle  the  first  time,  in  which  case  pro- 
ceed as  follows: 

On  the  line  g  c  lay  offgh  equal  to  the  calculated  width  of  the  port-opening,  and  draw  s  h.  From 
a,  draw  a  j  parallel  to  s  h  until  it  meets  g  c  produced  at  j.  Then  hj  will  be  approximately  the  length 
of  the  required  lap,  and  may  be  used  for  the  radius  of  the  new  lap  circle  k  id.  Find  point  I  in  the 
same  manner  that  g  was  found.  Then  t  I  should  equal  the  calculated  width  of  the  steam-port 
opening  within  -gV'.  If  it  does  not,  a  third  proportion  based  on  the  second  must  be  made. 

Then  a  t  is  the  required  lap  for  the  given  cut-off,  1 1  the  maximum  width  of  the  steam-port  open- 
ing, a  I  the  half -travel  of  the  valve,  and  v  a  I  the  angle  of  advance.  To  find  the  exhaust  lap  that 
will  give  release  at  the  assigned  time,  locate  the  crank  position  a  u  for  the  cross-head  at  r  (n  r  =  the 


FIG.  20. 

given  percentage  of  stroke).'  a  u  intersects  the  Zeuner  circle  a  x  at  w,  and  a  w  is  therefore  the  required 
exhaust  lap.  The  point  w  is  determined  exactly  by  drawing  from  x  a  perpendicular  to  a  u.  If 
the  crank  position  a  u  had  intersected  the  Zeuner  circle  a  I,  the  exhaust  lap  would  have  been  negative; 
that  is,  with  the  valve  in  its  central  position  the  steam-port  would  be  partly  open  and  in  commu- 
nication with  the  exhaust  port. 

Layout  of  Valve  and  Valve-Seat. 

Having  all  necessary  data,  the  head  end  of  the  valve  and  the  ports  may  now  be  laid  down  full 
size  as  follows:  Draw  the  valve-seat  line  Y  Z,  Fig.  20.  When  completed  the  valve  is  to  be  shown 
in  its  central  position. 

The  drawing  of  the  sectional  view  of  the  valve  and  ports  (Fig.  20)  is  to  be  made  full  size.  (This 
makes  three  separate  scales  to  be  used  in  this  problem,  namely;  the  crank  scale,  the  Zeuner  scale,  and 
the  valve  scale).  Therefore  from  any  convenient  point,  A,  on  Y  Z,  Fig.  20,  lay  off  A  T  =  at  of  Fig. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  19 

19  equal  to  the  steam-lap.  Lay  off  T  P  equal  to  the  calculated  width  of  the  steam-port,  and  P  W 
equal  to  the  exhaust-lap  as  found  at  a  w  in  Fig.  19.  T  L  is  the  maximum  steam-port  opening,  and 
equals  1 1,  Fig.  19.  .4  L,  Fig.  20,  then  equals  the  eccentricity,  or  l/>  the  travel  of  the  valve. 

Formula,  for  Minimum  Width  of  Bridge. 

The  width  of  the  bridge  P  R  should  in  all  cases  be  at  least  equal  to  the  thickness  of  the  cylinder 
wall,  in  order  to  secure  a  reliable  casting.  For  an  engine  of  this  size  this  thickness  may  be  Ys  "  to 
%"  according  to  judgment,  and  should  be  taken  within  this  range  unless  it  violates  the  following 
standard  rule : 

(Minimum)         (Width     }  (Width 

•j  width     of  j-   =   -j  of   port-  >•    +  Overtravel  +  %"  -  -   4  of  steam- 
(  bridge.       )          ( opening.  )  ( port. 

This  formula  will  affect  the  width  of  bridge  only  when  the  edge  A  of  the  valve  comes  within  ^ 
inch  of  the  edge  R  of  the  bridge,  and  applies  principally  in  repair  work.  The  amount  that  A  travels 
beyond  L  is  the  overtravel. 

Formula  for  Width  of  Exhaust  Port. 

R  V  is  the  width  of  the  exhaust  port,  and  must  be  so  taken  that  when  the  exhaust-lap  of  the 
valve  is  in  its  extreme  left-hand  position  there  will  still  be  a  width  left  at  least  equal  to  the  width 
of  the  steam-port.  R  V  may  thus  be  determined  graphically,  or  calculated  by  the  following  rule: 

Width  of   }         ( Maximum  )         (  Half-         )         (  Width       J         (  Width  ) 
exhaust        •    =  •<  inside  +    -j  travel        >•  +  •]  of  steam-  j-   -  -  •<  of 

port.  )          (  lap.  )         (  of  valve.   )         (  port.          )         (  bridge.  ) 

In  using  this  formula  it  must  be  kept  in  mind  that  the  exhaust-lap  may  be  different  on  the  two 
ends  of  the  valve,  according  to  the  conditions  of  the  problem,  and  that  therefore  the  size  of  both 
exhaust-laps  must  be  known,  and  the  greater  value  used  in  the  formula. 

Equalizing  Cut-Offs  by  Unequal  Steam-Laps. 

To  determine  the  exhaust  lap  on  the  crank  end  of  the  valve  it  will  now  be  necessary  to  con- 
sider the  conditions  affecting  the  crank  end,  as  follows : 

If  cut-off  occurs  at  the  same  percentage  of  the  forward  and  return  strokes  it  is  said  to  be  equal- 
ized. On  the  Zeuner  diagram,  already  used,  locate  the  crank  position  for  equalized  cut-off  on  the 
crank  end,  and  dot  in  the  corresponding  lap  circle.  The  diagram  will  now  show  that  equalized 
cut-off  obtained  in  this  way  gives  excessive  lead  on  the  crank  end,  and  is,  as  a  rule,  impracticable. 
It  will  not  be  used  in  this  problem,  but  the  "excessive  lead"  thus  obtained  should  be  marked  as 
such  on  the  diagram  for  future  reference. 

Another  method  of  equalizing  cut-off  without  obtaining  excessive  lead  will  be  described  on  a 
later  page. 

EQUALIZING  COMPRESSION  BY  UNEQUAL  EXHAUST-LAPS — SPECIAL  AND  GENERAL  CASES. 
The  steam-lap  on  the  crank  end  of  the  valve  is  to  be  made,  in  this  problem,  equal  to  that  on 
the  head  end,  and  the  crank  and  piston  positions  at  admission  and  cut-off  determined.  The  exhaust- 
lap  already  determined  for  the  head  end  fixes  the  exhaust  closure,  or  beginning  of  compression, 
for  that  end.  Now  determine  the  exhaust-lap  that  will  give  the  same  amount  of  compression  on 
the  crank  end  as  on  the  head  end.  Then  complete  the  design  of  the  crank  end  of  the  valve  as 
follows ; 


20 


Having  determined  R  V,  the  center-line  U  X  of  the  valve  and  ports  may  be  drawn.  The  area 
Q  of  the  cross-section  of  the  exhaust  port  may  be  made  equal  to  or  a  little  less  than  the  area  of  the 
steam-port.  The  edges  of  the  ports,  as  &tTB,PC,R  D,  etc.,  are  faced  surfaces,  while  the  remainder 
of  the  port  is  made  a  trifle  larger,  and  is  rough  cast.  The  valve-seat  should  be  limited,  as  at  E, 
so  that  the  edge  A  of  the  valve  will  overtravel  34"-  The  thickness  A  F  of  the  lap  is  generally 
made  about  the  same  as  the  bridge,  and  the  thickness  of  the  valve  wall  K  a  little  less. 

Place  the  necessary  working  dimensions  on  the  design  and  mark  the  finished  surfaces.  Tabu- 
late the  results  as  follows: 


Part  of  Stroke  completed  when 

Travel. 

Lead. 

Steam- 
lap. 

Exhaust 
lap. 

Steam- 
port 
opening. 

Admis- 
sion 
begins. 

Cut-off 
takes 
place. 

Release 
begins. 

Exhaust 
closure 
occurs. 

Head 

end. 

Crank 

end. 

EQUALIZATION  OF  RELEASE  AND  EXHAUST  CLOSURE  BY  UNEQUAL  EXHAUST  LAPS. 

Special  Case. 

If  a  valve  were  constructed  with  zero  exhaust-lap  on  each  end,  release  on  the  head  end  and 
compression  on  the  crank  end  would  occur  simultaneously  when  the  crank  is  in  the  position  o  b 


FIG.  21. 


tangent  to  the  Zeuner  circle  o  I,  Fig.  21.  The  same  would  be  true  for  release  on  the  crank  end 
and  compression  on  the  head  end,  with  the  crank  in  position  o  c  also  tangent  to  the  Zeuner  circle 
ol 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


21 


When  the  crank-pin  is  at  b  the  piston  is  at  b',  and  with  the  crank-pin  at  c  the  piston  is  at  c'.  j  k 
represents  the  stroke  of  the  piston,  j  b'  is  smaller  than  k  c' ,  and  therefore  neither  release  nor  com- 
pression is  equalized  on  the  forward  and  return  strokes  when  the  exhaust-lap  on  both  sides  is  zero, 
and  indicator  cards  from  the  two  ends  of  the  cylinder  will  not  be  similar. 

In  order  to  equalize  these  events,  assume  that  release  on  the  head  end  card  is  desired  when  the 
piston  is  at  d,  and  compression  when  at  e;  also  that  release  is  desired  on  the  crank  end  card  when 
the  piston  is  at  e,  and  compression  wljen  at  d.  Then  since  j  d  equals  k  e,  release  and  compression 
will  be  equalized  on  both  cards. 

With  d  as  a  center  and  a  radius  equal  to  the  connecting-rod,  locate  the  crank-pin  center  d'  cor- 
responding to  d;  locate  similarly,  e'.  By  drawing  the  crank  position  o  d',  we  find  that  the  valve  re- 
quires a  negative  exhaust-lap  equal  to  o/on  the  head  end;  similarly,  a  positive  exhaust-lap  equal  to 
o  g  is  required  on  the  crank  end.  In  this  particular  case,  and  when  j  d  and  k  e  are  comparatively 


H.£. 


FIG.  22. 


small,  of  and  o  g  will  be  so  nearly  equal  that  the  difference  in  values  cannot  be  detected  by  ordinary 
graphical  construction.  Thus  both  release  and  compression  are  equalized  on  the  forward  and  return 
strokes,  by  giving  negative  exhaust-lap  to  the  head  end,  and  an  equal  positive  exhaust-lap,  to  the 
crank  end  of  the  valve.  This  irregularity  in  the  construction  of  the  valve,  it  should  be  noted,  is  due 
to  the  effect  of  the  varying  angularity  of  the  connecting-rod,  referred  to  on  a  previous  page. 

General  Case. 

The  above  is  a  special  and  simple  case,  and  only  applies  when  release  and  compression  both  occur 
at  the  same  percentage  of  the  stroke.  In  ordinary  practice,  as  a  rule,  release  occurs  later  than  com- 
pression, and  in  such  cases  equalization  of  both  compression  and  release  are  obtained  approximately 
as  follows : 

In  Fig.  22  assume  that  the  valve  design  has  been  completed  in  all  respects,  except  the  determina- 
tion of  the  exhaust  laps.     Then  the  angle  of  advance,  valve-travel,  etc.,  are  known. 
Assume  release  on  forward  stroke  (head  end  card)  at  /,  and 

"       "    return        "       (crank  end  card)  at  g.     (fb  =  gc). 


22 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


Also  assume  compression  on  forward  stroke  (crank  end  card)  at  d,  and 

"  return          "     (head  end  card)    "  e.     (d  b  =  e  c). 

The  crank-pin  positions  for  the  piston  positions/,  g,  d  and  e,  may  be  found  at/'  g'  d'  and  e'.  Draw 
.the  corresponding  crank  positions  shown  by  the  dotted  lines.  Then  the  necessary  exhaust-lap  for 
release  (head  end  card)  at  af  is  a  k,  and  the  necessary  exhaust-lap  for  compression  (head  end  card) 
at  ae'  is  a  I. 

But  the  exhaust-lap  at  the  head  end  of  the  valve  cannot  h^ve  the  two  different  values  a  k  and  a  I 
at  the  same  time.  Therefore  a  compromise  is  taken  by  making  the  head  end  exhaust-lap  =  l/% 
(a  k  +  a  I)  =  a  m  =  a  n. 

Drawing  crank  lines  through  a  m  and  a  n,  the  corresponding  crank-pin  positions  o  and  p  and  pis- 


Va/re  stem 


FiG.123. 


FiG.f25. 


FIG.  24. 


FIG.  26. 


ton  positions  o'  and  p'  may  be  obtained,  o'  being  release  on  head  end  card,  and  p'  compression  head 
end  card. 

In  the  same  way  the  compromise  lap  on  the  crank  end  of  the  valve  will  be  =  Y^  (aq  -\-  a  r)  = 
a  s  =  a  t,  and  release  will  occur  at  v'  and  compression  at  u' ' . 

p'  c  and  u'  b  will  now  be  found  to  be  approximately  equal,  and  the  compression  on  the  two  ends 
practically  equalized,  but  not  by  the  same  amount  as  originally  laid  down  at  d  b  and  e  c.  If  a  defi- 
nite compression  were  desired  it  would  have  to  be  found  by  drawing  another  trial  diagram  similar  to 
Fig.  22. 

Also  the  distance  o'  b  and  v'  c  are  approximately  equal,  and  the  release  on  the  two  ends  thus  prac- 
tically equalized,  but  again  not  by  the  same  amount  as  originally  laid  down  at  /  6  and  g  c. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


23 


ROCKER-ARMS,  STRAIGHT  AND  BENT,  AND  THEIR  EFFECT  ON  VALVE-TRAVEL  AND  STEAM  DISTRIBU- 
TION. 

Types  of  Rocker- Arms. 

The  principal  types  of  rockers  are  shown  in  Figs.  23  to  26.  Fig.  23  shows  simply  a  mul- 
tiplying rocker  for  accommodating  a  given  location  of  valve-stem  which  would  otherwise  require 
excessive  angularity,  or  an  extremely  large  eccentric  sheave  and  strap.  The  rocker  in  Fig.  24  accom- 
plishes all  the  above  and  in  addition  equalizes  cut-off  with  equal  lead  when  laid  out  in  accordance 
with  the  directions  on  the  following  pages.  The  rockers,  shown  in  Figs.  25  and  26,  will  do  all  that 
the  ones  in  Figs.  23  and  24  will  do,  and,  in  addition,  will  produce  a  different  direction  of  rotation  of  the 
shaft,  or,  in  other  words,  will  reverse  the  direction  of  running  of  the  engine,  as  shown  by  the  arrows,  r. 

It  was  pointed  out  in  the  directions  for  drafting-table,  Prob.  1  (p.  17),  that  the  cut-off  could  be 
equalized  on  the  two  ends  of  the  cylinder  by  placing  unequal  steam-laps  on  the  valve,  but  that  this 
method  was  objectionable  for  the  reason  that  it  gave  very  unequal  leads. 


FIG.  27. — Showing  valve  in  central  position. 


Another  method  for  obtaining  equalized  cut-off,  and  at  the  same  time  retaining  practically  equal 
leads,  is  by  means  of  the  bent  rocker.  This  method  permits  the  use  of  equal  steam-laps  on  the  valve. 

Equalizing  Cut-Off  by  a  Valve  Having  Equal  Steam-Laps. 

In  laying  out  the  Zeuner  or  other  valve  diagram  for  a  required  valve  motion,  no  attention  what- 
ever is  paid  to  the  rocker-arm.  The  diagram  is  always  laid  out  originally  as  if  the  eccentric-rod  were 
directly  connected  to  the  valve-stem.  Allowance  for  the  multiplying  action  due  to  unequal  lengths 
of  rocker-arms  is  made  in  the  layout  described  in  the  following  pages. 

The  action  of  the  rocker  and  the  effect  it  has  on  the  motion  of  the  valve  may  best  be  shown  by  a 
practical  application.  Keeping  in  mind  the  fact  that  the  valve  must  be  the  same  distance  off  center 
when  admission  begins  as  it  is  when  cut-off  takes  place  (only  going  in  opposite  direction) ,  it  may  be 
said  in  a  general  way  that  the  rocker  is  proportioned  and  situated  so  as  to  have  the  valve  in  this  place 
at  the  proper  times,  despite  the  effect  of  the  unsymmetrical  motion  produced  by  the  varying  angu- 
larity of  the  connecting-rod.  In  other  words,  a  bent  rocker  is  a  piece  of  mechanism  producing  irreg- 
ular motion,  deliberately  introduced  to  counterbalance  the  irregular  motion  produced  by  the  con- 
necting-rod. Let  Fig.  27  represent  the  valve  and  valve-seat. 


24 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


In  Fig.  28,  a  d  is  the  crank  position  for  admission,  head  end. 
ae   "     "       "          "  "  "  crank" 

af    "     "      "          "          "  %  cut-off,  head    " 
ag  "     "       "          "          "  %       "      crank     " 

The  circle  d'  f  e'  g'  is  the  eccentric  circle  drawn  to  the  same  scale  as  the  crank  circle.     The  angle 
dad'  equals  the  angle  between  the  crank  and  eccentric.     Therefore, 
the  eccentric  center  is  at  d'  when  admission  occurs  at  a  d,  head  end 

/'       "     cut-off  "       "   af      " 

e'        "     admission       "       "   a  e  crank  end 


K       (I 

II     (( 


<l 


cut-off 


a  g 


G.E. 


Showing  effeof  of  a  rocker 
on  the  va/ve  trave/  and  on 
the  steam    distribution. 


FIG.  28. 

With  d'  and  /'  as  centers  and  a  radius  equal  to  the  eccentric-rod  (in  this  case  taken  equal  to  the 
connecting-rod)  draw  the  arcs  intersecting  at  I.  Again  with  e'  and  g'  as  centers  draw  the  arcs 
intersecting  at  m. 

I  is  position  for  n  of  rocker-arm  for  admission  and  cut-off,  head  end 

m         "        "    "  "          "  "          "  "        "        crank  " 

Let  n  bisect  distance  I  m,  and  n  o  be  drawn  perpendicular  to  I  m.  The  point  o  represents  the 
rocker-arm  shaft,  and  its  actual  location  must  be  such  as  to  afford  a  convenient  attachment  of  the 
bearing  to  the  frame  of  the  engine,  o  is  assumed  here.  When  the  rocker-arm  is  in  the  position 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS  25 

n  o  the  valve  is  central.  While  the  end  n  of  the  arm  is  going  from  n  to  I  the  valve  must  travel  to 
the  left,  a  distance  equal  to  the  steam-lap,  and  the  arm  n"  o  of  the  rocker  must  be  proportioned  so 
as  to  secure  this  result.  This  is  done  by  making  n  o  :  n"  o  :  :  n  I  :  steam-lap,  n"  will  be  the  end 
of  the  valve-stem  for  central  position.  The  center  o  for  the  rock-shaft  should  be  taken  so  that 
the  arc  I  m  when  prolonged  in  both  directions  will  intersect  the  arcs  at  r'  and  s'  drawn  with  r  and  s 
as  centers,  and  the  length  of  the  eccentric-rod  as  a  radius*.  These  latter  arcs  contain  the  extreme 
positions  of  the  eccentric-rod,  and  limit  the  arc  through  which  the  point  n  oscillates.  They  also 
determine  the  total  travel  of  the  valve,  and  on  this  account  n  r'  and  n  sf  should  be  made  as  nearly 
equal  as  possible,  .and  also  as  short  as  is  consistent  with  the  necessary  valve-travel.  This  latter 
may  be  determined  by  finding  rf",  n"  and  s'".  Then  the  horizontal  distances  between  r'"  and  n", 
and  between  n"  and  s'"  must  at  least  equal  the  original  half -travel  of  the  valve;  otherwise  there 
might  be  a  contracted  steam-port  opening,  o,  as  already  stated,  must  be  a  convenient  point  on 
the  engine  frame,  and  the  horizontal  line  through  I'  and  m'  must  be  at  the  elevation  of  the  valve- 
stem,  o  could  be  placed  on  the  opposite  side  of  I  m  without  affecting  the  equalization  of  admission 
or  cut-off. 

Unequal  Valve  Travel  on  Head  and  Crank  Ends  Due  to  Rocker. 

The  introduction  of  the  rocker  has  not  only  changed  the  total  travel  of  the  valve  (compare  r  s 
with  r'"  s'"),  but  has  made  the  travel  from  the  central  position  unequal  on  the  head  and  crank 
ends.  This  change  in  travel  may  seriously  affect  some  of  the  other  events  in  the  stroke,  and  must 
be  looked  into  before  the  design  is  considered  finished.  The  effect  in  this  case  is  shown  in  Figs. 
27  and  28  as  follows: 

With  rocker,  the  travel,  of  the  valve  to  the  left  =  ft"  r'"  =  a  z  (on  enlarged  scale) ,  Fig.  28;  equals 
also  a  z,  Fig.  27.  Without  the  rocker  this  travel  is  a  h  in  both  Figs.  27  and  28.  The  increase  is 
therefore  h  z,  and  there  is  overtravel  =  h  z.  The  inside  lap  of  the  valve  will  go  to  j,  Fig.  27  (i  j 
=  a  z),  and  the  exhaust  port-opening  will  be  contracted  to  j  k,  which  is  less  than  the  width  of  the 
steam-port,  (y  y'  =  width  of  steam-port)  and  which  will  therefore  interfere  with  a  free  exhaust  of 
steam.  In  such  case  the  exhaust  port  must  be  widened  and  the  valve  lengthened  to  correspond. 
Such  alteration  does  not  interfere  with  the  steam  distribution. 

Zeuner  Circles  Changed  to  Irregular  Closed  Curves  by  Rocker. 

From  the  foregoing  it  is  evident  that  the  Zeuner  circles  used,  in  designing  the  valve,  do  not  show 
the  true  valve-travel,  or  the  complete  true  steam  distribution,  when  the  rocker  is  added  to  the 
valve-gear.  To  show  this,  the  dotted  closed  curves  a  v  z  w  and  a  1  2  x  would  have  to  be  drawn. 
av  =  aw  =  al  =  a  x  (all  on  enlarged  scale)  =  I' n"  =  n"  m'  (both  on  full  size  scale).  Also 
n"  r'"  =  a  z  and  n"  s'"  =  a  2  when  brought  to  the  same  scale.  Intermediate  points  on  the  dotted 
curves  may  be  determined  by  taking  successive  positions  of  the  crank  and  finding  the  correspond- 
ing distances  the  end  of  the  valve-stem  n"  is  off  center,  and  setting  these  distances  off  on  the  crank 
positions.  The  maximum  crank-end  travel  of  the  valve,  in  this  case,  happens  to  be  the  same  with 
the  rocker  as  without. 

It  will  be  observed  that  the  effects  of  the  different  exhaust-laps  which  give  equalized  compres- 
sion, Fig.  28,  are  very  slightly  changed  by  introducing  the  bent  rocker.  This  is  shown  by  the 
dotted  curves  agreeing  very  closely  with  the  original  Zeuner  circles  within  the  limits  of  the  radii 
of  the  exhaust-lap  arcs,  a  3  and  a  4. 

*  To  be  exact  the  arcs  at  r'  and  s'  should  be  the  envelopes  of  a  series  of  arcs  drawn  with  centers  on  either  side  of 
r  and  s. 


26 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


In  some  problems  it  may  be  possible  to  design  the  rocker  so  that  a  symmetrical  valve  will  equal- 
ize exhaust  and  compression  in  addition  to  equalizing  cut-off  and  lead,  as  follows: — Locate  point 
5,  Fig.  28,  in  the  same  way  that  I  was  found  only  using  the  eccentric  center  positions  at  release 
and  compression,  headend.  Also  locate  point  6  for  the  crank  end.  If,  in  addition  to  the  con- 


ic.o. 


f' 


A  DM.4  CO., 


A  DM.  %  C  0 


\COMP.j:  C_0 

COMP  ic  a 


FIG.  29.— Showing  Effects  of  Early  Cut-Off  with  a  Plain  D  Slide-Valve. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  27 

siderations  already  mentioned  for  determining  the  position  of  the  rock-shaft  o,  the  arc  passing 
through  /  and  m  can  be  made  to  include  the  points  5  and  6,  so  that  they  are  symmetrical  with 
respect  to  n,  the  equalization  will  be  accomplished.  With  zero  inside  lap  there  will  be  only  one 
point  instead  of  5  and  6,  and  this  may  be  made  to  fall  on  the  arc  I  m  at  n,  and  then  all  four  events 
would  be  equalized  with  a  symmetrical  valve,  by  the  rocker. 

LIMITED  USE  OF  THE  PLAIN  D- VALVE. 

On  page  2  of  these  directions  it  was  pointed  out  that  a  plain  slide-valve  with  zero  steam-lap 
admitted  steam  to  the  engine  cylinder  during  the  full  stroke.  Also  that  to  cut  off  the  admission 
of  steam  before  the  end  of  the  stroke,  steam-lap  had  to  be  added  to  the  valve.  This  suggests 
the  fact  that  the  earlier  the  cut-off  the  larger  the  steam-lap  must  be.  When  steam-lap  becomes 
too  large  the  economical  working  of  the  engine  is  seriously  affected,  and  the  plain  D-valve,  as  shown 
in  Fig.  27,  can  no  longer  be  used  economically.  The  effect  of  early  cut-off  is  shown  in  Fig.  29. 

Let  the  dotted  construction  be  the  Zeuner  diagram  for  an  engine  having  %  cut-off,  port-opening 
=  ef,  and  lead  =  c  d.  Let  the  solid  construction  be  the  Zeuner  diagram  for  the  same  engine  with  % 
cut-off,  and  with  the  port-opening  and  lead  the  same  as  for  %  cut-off.  Then  er  f  =  ef  and  c'  d'  =  c  d. 

The  lap  necessary  for  %  cut-off  is  a  b.  For  %  cut-off  it  is  found  to  be  a  g.  The  half-valve 
travel  for  %  cut-off  is  af  and  for  ^  cut-off  it  is  af.  An  increase  in  valve-travel,  as  may  be  seen  from 
Fig.  27,  calls  for  a  wider  exhaust\port  and  therefore  a  larger  valve.  A  larger  valve  has  additional 
area  exposed  to  steam  pressure  and  also  greater  weight  of  itself,  thus  giving  an  increased  amount  of 
sliding  friction.  The  additional  weight  and  friction  also  affect  the  sensitive  action  of  the  governor. 

Still  further,  in  Fig.  29,  it  may  be  seen  that  for  the  earlier  cut-off  the  release  and  compression  are 
both  earlier.  (The  exhaust-lap  a  h  has  remained  the  same  for  %  and  ^  cut-off) .  If  the  attempt  is 
made  to  correct  the  release  so  as  to  make  it  later  by  increasing  the  exhaust-lap,  the  compression  is 
made  still  earlier. 

The  above  considerations  affecting  the  action  of  the  plain  D-valve  have  established  a  limit  to 
which,  in  its  simple  form,  it  may  be  economically  used.  It  is  sometimes  employed  for  cut-off  at }/%, 
but  as  a  rule  not  earlier  than  %  stroke  with  a  fixed  eccentric. 

SPECIAL  VALVE  EXERCISE. 

In  addition  to  drafting-table  problem  1,  and  the  several  exercises  given  on  pages  11,  12  and  13, 
the  following  useful  construction  by  Welch  in  his  treatise  on  "Valve-Gears"  should  be  noted: 

Given:  Valve-travel,  position  of  crank  for  cut-off,  and  lead.     See  Fig.  30. 

Find:  Lap  and  angle  of  advance. 

A  B  =  y%  valve-travel. 

A  P  =  Position  of  crank  at  cut-off. 

With  A  as  a  center  and  A  B  as  a  radius,  draw  a  circle  intersecting  the  horizontal  line  A  J  at  D. 
With  D  as  a  center  and  a  radius  equal  the  lead,  draw  the  "lead-circle"  T  H  J. 

From  P  draw  line  P  K  tangent  to  the  lead-circle. 

Draw  A  K.     Draw  the  circle  V  Z,  R  tangent  to  P  K. 

Then  V  Z  R  =  lap  circle.     Draw  A  E  1  to  P  K. 

Then  <  B  A  E  =  Angle  of  advance. 

A  K  =  Position  of  crank  at  admission  and  Q  L  =  D  T  =  lead. 

Proof  That  Q  L  =  D  T. 

Draw  E  R  and  E  L  ]_  to  A  K  and  A  D  respectively. 

Draw  D  F  parallel  to  K  Z.     Draw  D  H  parallel  and  equal  to  F  Z. 

In  ^  E  A  R  and  K  A  Z;  E  A  =  A  K,  <  EAR  is  common,  and  A  E  RA&ndK  ZA  are  right -4. 


28  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

/ .  ^  E  A  R  and  K  A  Z  are  equal,  and  A  Z  =  A  R.    Also  A.Q/  =  AR  =  AZby  construction. 
In  /^E  A  Land  DA  F;  E  A  =  A  D,  <  E  A  D  is  common,  and^EL  A  andD  FA  are  right  ^. 
/ .  A  E  A  L  and  D  A  F  are  equal  and  F  A  =  A  L. 
:.QL  =  FZ.    But  F  Z  =  D  H  =  T  D  by  construction. 
.' .  Q  L  =  T  D  =  lead. 


THE  ALLEN  VALVE. 

This  valve  is  the  type  common  in  locomotive  work.  With  a  given  travel  it  admits  twice  as  much 
steam  as  the  ordinary  valve.  For  example,  in  Fig.  31,  the  valve  is  in  its  extreme  right-hand  position, 
having  moved  a  distance  equal  to  the  lap  +  ^  the  port-opening,  6  c.  With  this  half -travel  the  port- 
opening  is  \b  c  +  d  e)  or  2  6  c.  The  steam-lap  =  k  c  —  h  b  which  should  be  equal  to,  or  greater  than 
c  e  in  order  to  keep  the  two  ends  of  the  cylinder  from  being  in  communication  through  the  passageway 
in  the  valve.  The  edges  of  the  valve-seat,  a  and  m,  must  have  special  consideration  in  this  type  of 
valve,  namely,  that  r  on  the  valve  must  pass  m  on  the  valve-seat  exactly  at  the  same  time  that  c  on 
the  other  end  of  the  valve  is  passing  b.  A  top  view  of  the  Allen  valve,  or  "trick  valve"  as  it  is  some- 
times called,  with  so  much  of  the  valve-seat  as  is  visible,  is  shown  on  reduced  scale  in  Fig.  31a. 

DRAFTING  TABLE  PROBLEM,  No.  II.     DESIGN  FOR  AN  ALLEN  VALVE. 

Let  it  be  required  to  design  an  Allen  valve  for  an  engine  having  a ....  inch  bore, ....  inch  stroke, 
running  at ....  revolutions  per  minute  and  cutting  off  at ....  stroke  on  both  ends,  with ....  inch  lead 
on  head  end.  Use  zero  exhaust-lap  on  both  ends.  The  steam-port  may  be  taken  .7  of  the  bore. 
The  connecting-rod  may  be  taken  5  times  the  crank  length. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


29 


The  first  step  in  this  design  consists,  as  in  problem  I,  in  calculating  the  width  of  port-opening, 
and  width  of  steam-port.  Then  lay  out  the  crank  circle  and  cross-head  travel  to  the  largest  regular 
scale  that  the  drawing  paper  will  allow.  Judgment  must  be  used  in  determining  the  scale  for  the 
Zeuner  diagram,  based  on  the  principle  that  the  largest  convenient  scale  for  geometrical  drawings, 
gives  the  greatest  accuracy. 

Effect  of  Two  Admission-  and  Two  Lead- Areas  on  Zeuner  Diagram  Construction. 
The  %  valve-travel  in  drafting-table  problem,  I,  was  equal  to  the  lap  -f-  the  whole  width  of  the 
steam-port  opening.  In  this  problem  it  is  equal  to  the  lap  +  J/^  the  calculated  width  of  the  steam- 
port  opening,  because  the  Allen  valve  is  in  effect  two  plain  D-valves  combined,  and  admits  steam  to 
the  same  steam-port  through  two  openings  at  the  same  time.  Each  opening  then  takes  care  of  3/2 
the  lead,  and  in  laying  out  the  Zeuner  diagram  for  the  Allen  valve  only  3/£  the  given  lead  as  well  as  Yi 
the  calculated  width  of  the  steam-port  opening  is  considered.  When  the  Zeuner  diagram  is  com- 
pleted, designate  the  crank  positions  in  the  manner  shown  in  Fig.  29. 


FIG.  31a. — Top  view  of 

Allen  valve  and 

valve  seat. 


FIG.  31. — Allen  Valve.    Section  on  x  y  of  FIG.  3  la. 

The  valve  may  now  be  laid  out  full  size.  Starting  with  the  point  6,  Fig.  32,  which  is  an  illus- 
tration for  a  general  case,  6  e-  =  steam-lap.  6  c  =  thickness  of  flange  of  the  outside  valve  wall, 
which  should  be  a  little  wider  than  the  valve  wall  to  allow  for  facing,  and  small  enough  so  that 
6  c  +  c  d  is  equal  to  or  less  than  the  steam-lap :  otherwise  the  two  ends  of  the  cylinder  might  be 
in  communication  through  the  auxiliary  passage  X  for  an  instant.  If  c  6  should  come  so  small 
as  to  prevent  a  good  casting,  some  one  or  more  conditions  of  the  design  would  have  to  be  changed. 

c  d  =  Yi  width  of  calculated  steam-port  opening. 

ef*=2cd  +  bc. 

f  g  =  exhaust-lap. 

f  h  =  width  of  bridge  =  y8"  for  engine  given  in  this  problem. 

h  i  =  3/2  width  of  exhaust  port. 

*  When  ej  is  much  larger  than  the  calculated  width  of  port,  it  may  be  reduced  to  the  correct  size  in  some  such  way 
as  shown  by  the  dotted  lines  at  k  and  I  ( =•  calculated  width  of  port)  in  Fig.  32;  or,  a  face-plate  may  be  used.  These 
dotted  lines  are  not  to  be  drawn  by  the  student. 


30 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


Total  width  of   exhaust  port  =  maximum   exhaust-lap  +  3/2  travel  of  valve  -f-  width  of  .steam- 
port  —  width  of  bridge. 

The  location  of  the  point  a  is  important,  for  just  as  the  point  corresponding  to  b  on  the  other 
end  of  the  valve  is  uncovering  the  point  corresponding  to  e,  the  point  c  must  be  uncovering  a.  There- 
fore c  a  must  equal  the  steam-lap  on  the  other  end  of  the  valve. 


FIG.  32. 

It  will  be  evident  that  y  must  be  at  least  equal  to  c  d  so  as  to  give  free  admission  to  the  valve 
passage  X.  It  may  be  made  equal  to  c  d  +  H  "• 

X  may  also  be  made  equal  to  c  d  -f  1A  "  to  allow  for  friction  of  steam  in  the  rough  cored  passage- 
way. 

i  j  may  be  taken  =  Yi  (calculated  width  of  steam-port  -+-  width  of  exhaust-port.) 

All  the  remaining  dimensions  necessary  to  complete  the  design  are  independent  of  the  action 
of  the  valve  so  far  as  steam  distribution  is  concerned,  and  are  determined  solely  according  to  the 
size  of  the  valve.  For  this  problem  they  may  be  taken  as  shown  in  Fig.  32. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


31 


Locomotive  Balanced  Valve. 

The  Allen  valve  may  be  converted  into  the  ordinary  locomotive  balanced  valve  by  adding 
metal  in  the  form  of  the  dotted  lines  shown  at  the  top  of  the  valve,  which  the  student  should  do.  q 
is  a  slot  containing  a  rectangular  bar  which  is  kept  against  the  faced  surface  of  the  cover  of  the 
steam-chest,  as  the  valve  slides  back  and  forth,  by  means  of  a  spring  at  r.  This  slot  and  the  bars 
extend  all  around  the  valve,  and  keep  the  live-steam  pressure  from  exerting  its  power  to  press  on 
the  back  or  top  of  the  valve  and  thus  force  it  against  the  valve-seat  with  greatly  increased  friction. 
In  the  locomotive  balanced  valve  there  is  a  small  hole  through  the  center  communicating  with  the 
exhaust.  This  carries  off  any  live  steam  that  may  leak  through. 

Place  the  necessary  working  dimensions  and  mark  the  finished  surfaces  on  the  design. 
Tabulate  the  results  as  in  drafting-table  problem,  No.  1. 

Limited  Use  of  the  Allen  Valve. 

That  the  Allen  valve  cannot  be  used  to  advantage  for  cut-off  much  later  than  half  stroke  with 
a  fixed  eccentric  may  be  seen  by  referring  to  Figs.  33-36.  A  valve  is  shown  in  part  section 


Fig.33 


Fig.  35 


Tl 


Fig.  34. 


Fig.  36 


in  Fig.  34  and  its  corresponding  Zeuner  diagram  is  shown  in  Fig.  33,  both  illustrations  being  to  the 
same  scale  and  similarly  lettered.  It  will  be  noted  that  the  lap,  a  e,  is  large  enough  to  contain 
the  valve-wall  thickness,  c  e,  the  passageway,  b  c,  equal  to  e  /,  and  to  have  some  space,  b  a,  left 
over.  But  in  Fig.  35,  let  the  cut-off  be  assumed  at  a  m,  keeping  the  same  lead  and  lap;  then  the  single 
port  opening  becomes  p  n.  If  now  the  necessary  valve-wall  thickness  is  laid  off  equal  to  say  p  q, 
it  is  found  that  there  is  not  enough  room  in  the  steam-lap  for  another  passageway  equal  to  p  n, 
and  therefore  that  cut-off  as  late  as  a  m  is  not  possible  with  an  Allen  valve  having  the  data  here 
used  and  direct-connected  by  a  "fixed"  eccentric.  With  special  forms  of  valve  gears  and  governors, 
the  travel  of  the  valve  and  the  angle  of  advance  may  be  varied  automatically,  and  the  cut-off 
made  later,  as  will  be  shown  when  the  different  forms  of  valve  gears  and  governors  are  taken  up. 


32 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


SECTION   II.— VALVE  DIAGRAMS. 

In  addition  to  the  Zeuner  diagram  a  number  of  methods  have  been  devised  to  show  graphically 
the  relative  positions  of  the  valve  and  crank  at  any  instant.  A  brief  description  of  the  more  im- 
portant diagrams  will  be  given. 

BILGRAM  DIAGRAM. 

Let  it  be  considered  that  the  crank  is  on  the  head  end  dead-center  on  the  line  a  b,  Fig  37,  and 
turning  in  the  direction  shown  by  the  arrow.  Also  let  the  distance  a  b  represent  the  }/2  valve- 


FIG.  37. 


travel,  and  draw  the  eccentric  center  circle  h  b  c.     Then  on  the  opposite  side  of  the  crank  lay  off 
the  angle  c  a  d  =  the  angle  of  advance. 

From  d  draw  the  line  d  e  perpendicular  to  the  crank  position  b  a  prolonged,  and  d  e  will  be  the 
distance  the  valve  is  off  center  when  the  crank  is  at  a  b.  Likewise, 

when  the  crank  is  at  a  f  the  valve  is  off  center  d  g,  and 

"       "       "       "   "  a  h    "       "      "    "       "       da  (maximum  distance) 
"       "       "       "   "ad    "       "     "     central. 

The  reason  for  these  facts  may  be  found  in  Fig.  38,  where  a'/'  is  an  assumed  position  of  the  crank, 
and  a'  z  the  corresponding  eccentric  position,  with  x  a'  z  ( =  cad,  Fig.  27)  as  the  angle  of  advance. 
Then  with  the  crank  at  a'  f  the  valve  is  off  center  a  distance  z  y.  It  remains  to  show  that  z  y  =  d'  g' . 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


33 


<  x  a'  z  =  <  d'  a'  c'  =  angle  of  advance.  Since  £  a'  is  1  to  a'  w,  and  v  a'  1  to  a'  c' ,  the 
<  x  a'  v  =  <  c'  a'  w.  Therefore  <  d'  a'  w  =  <  z  a'  v.  Also  A  d'  g'  a'  and  z  y  a'  are  right  angles, 
and  the  ^  d'  a'  g'  and  z  a'  y  are  equal.  .'.  y  z  =  d'  g'. 

Since  d  g,  Fig.  37,  equals  the  distance  the  valve  is  off  center,  it  is  only  necessary  to  draw  a  circle 
with  d  k  ( =  the  steam-lap)  as  a  radius  and 
k  g  will  equal  the  steam-port  opening  for  the 
crank  position  a  f. 

I  e  =  the  lead,  a  m',  drawn  with  its  pro- 
longation tangent  to  the  steam-lap  circle,  is 
the  position  of  the  crank  for  admission. 
a  n,  also  tangent  to  the  steam-lap  circle,  is 
the  cut-off  position. 

If  the  valve  has  an  exhaust-lap  d  o,  the 
exhaust-lap  circle  should  be  drawn  with  a 
radius  =  d  o,  and  then  a  o,  tangent  to  it, 
will  be  the  crank  position  for  release. 
Likewise  a  i',  with  its  prolongation  tangent 
to  the  exhaust-lap  circle,  will  be  the  position 
for  compression. 

For  the  crank  end  of  the  cylinder  a  m  is 
admission;  a  n'  cut-off;  a  o'  release,  and  a  r 
compression.     In   Fig.    37   the   steam   and 
exhaust-lap  circles  are  taken  the  same  on 
both  the  head  and  crank  ends. 
$  If  the  head  end  exhaust-lap  had  been  negative,  a  r  instead  of  a  o  would  have  been  the  release 
.-position  for  the  head  end. 

Solution  of  Drafting  Table  Problem  No.  1  by  Bilgram  Diagram. 

Drafting  table  problem  1,  of  this  course,  would  be  solved  by  the  Bilgram  diagram  as  follows: 

Given:  Cut-off,  release,  lead,  and  steam-port  opening.  To  find:  Steam  and  exhaust-laps,  travel 
of  valve,  and  crank  positions  for  the  events  of  the  stroke. 

In  Fig.  39  draw  line  c  b  for  center-line  of  engine.  At  any  point  a  draw  a  n  for  the  given  cut-off 
position.  Draw  line  s  t  parallel  to  c  b  and  a  distance  from  it  equal  to  the  lead.  Draw  arc  u  v  about 
a  as  a  center  with  the  calculated  width  of  steam-port  opening  as  a  radius.  Find  by  trial  the  center, 
d,  of  a  circle  that  will  be  tangent  to  a  n,  s  t,  and  the  arc  u  v. 

Then  d  I  is  the  required  steam-lap.  Draw  a  o  for  the  given  release  position,  and  determine  the 
exhaust-lap  by  drawing  a  circle  with  d  as  a  center  and  tangent  to  a  o. 

If  d  w  represents  the  necessary  exhaust-lap  circle  for  the  crank  end  to  give  equalized  compression, 
as  called  for  in  drafting-table  problem  1,  then  the  events  of  the  stroke  are  as  follows: 


FIG.  38. 


Admission. 

Cut-Off. 

Release. 

Compression. 

Head  end 
Crank  end 

a  m 
a  q 

a  n 
a  x 

a  o 
ay 

ag 

a  z 

FIG.  39. 


FIG.  40. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 
REULKAUX  DIAGRAM. 


35 


In  making  use  of  this  diagram  let  the  indefinite  line  cab,  Fig.  40,  be  the  center-line  of  the  engine, 
and  at  any  point,  a,  draw  a  z  perpendicular  to  it.  Draw  the  circle  czb  with  a  radius  equal  to  the  Y^. 
travel  of  the  valve,  and  lay  out  the  angles  z  a  h  and  bad'  each  equal  to  the  angle  of  advance.  Then 
for  any  position  of  the  crank  such  as  a /,  it  is  only  necessary  to  draw  from/,  the  point  where  the  crank 
line  crosses  the  valve  circle  a,  perpendicular  to  the  line  a  d'  limiting  the  angle  of  advance,  to  find  the 
distance  /  g  that  the  valve  is  off  center. 

This  may  be  proven  by  reference  to  Fig.  38,  where  a'  f  is  a  given  crank  position  and  d'  e  the  line 
limiting  the  angle  of  advance  (=  V  a'  e).  Since  z  is  the  eccentric-center  position  for  the  crank 
position  a'  f,  zyis  the  distance  the  valve  is  off  center.  It  is  only  necessary  to  demonstrate  that 
/'  J '  =  z  y-  This  is  readily  done  for  the  reason  that  in  the  right-angle  triangles,  za'  y  and/'  a'  j,  the 
sides  a'  z  and  a'  f  are  equal,  and  the  angles  za'  y  and/'  a'  j  are  equal.  (Angle  6'  a'  e  —  angle  z  a'  x  = 
angle  of  advance;  and  angle  b'  a'  f  =  angle  x  a' v,  the  sides  being  respectively  perpendicular). 
Therefore  the  triangles  are  equal,  and/'/  =  z  y  =  distance  the  valve  is  off  center  for  crank  posi- 
tion a'  f. 

In  Fig.  40  draw  the  line  n  m'  parallel  to  dad'  and  at  a  distance  from  it  equal  to  the  steam-lap  = 
a  p.  Then  for  any  crank  position  such  as  af  the  steam-port  is  open  f  k.  ap  =  the  steam-lap  for 
one  end  of  the  valve,  and  a  p'  the  steam-lap  for  the  other  end.  In  this  case  they  are  equal. 

Likewise  a  I  =  the  exhaust-lap  for  one  end,  and  a  I'  for  the  other.  Lines  drawn  through  I  and  I' 
parallel  to  d  d'  are  the  exhaust-lap  lines. 

The  events  of  the  stroke  according  to  the  Reuleaux  diagram,  occur  as  follows: 


Admission. 

Cut-Off. 

Release. 

Compression. 

Head  end 
Crank  end 

a  m' 
a  m 

a  n 
a  n' 

a  o 
a  o' 

ar' 
ar 

b  e  is  the  lead  for  the  head  end,  and  c  q  for  the  crank  end. 

VALVE  ELLIPSE. 

The  valve  ellipse  is  a  curve  in  which  the  ordinates  show  the  amount  the  valve  is  off  center;  and  the. 
abscissae,  the  corresponding  piston  positions. 

It  may  be  obtained,  as  in  Fig.  41,  by  dividing  the  cross-head  travel  into  an  equal  number  of 
parts  as  at  1,  2,  3,  etc.  With  these  divisions  as  centers,  and  with  a  radius  equal  to  the  length  of 
the  connecting-rod,  strike  arcs  intersecting  the  crank-pin  circle  in  the  points  1',  2',  3',  etc. 

a  r  is  the  radius  of  the  eccentric-center  circle,  and  the  angle  o'  a  r  is  the  angle  between  the  crank 
and  the  eccentric.  The  points  r  e  f  g,  etc.,  show  the  eccentric-center  positions  for  the  correspond- 
ing crank-pin  positions  0',  1',  2',  3',  etc. 

Then  with  piston  at  0  the  valve  is  off  center  the  distance  r  h  =  o'  I 


1 


e      = 


"  "       "  2     "      "      "    "       "        "         "        /  7  =  c  n 

etc.,  and  these  values,  o'  I,  d  m,  c  n,  etc.,  laid  off  on  the  piston  position  ordinates  through  o',  d 
c,  etc.,  in  the  valve  ellipse  diagram  determine  the  points  on  the  valve  ellipse.  The  points  d,  c, 
b,  etc.,  are  equally  spaced  the  same  as  the  points,  1,  2,  3,  etc.,  in  the  cross-head  stroke. 

The  curve  generated  in  this  way,  although  called  the  "valve  ellipse,"  is  not  a  true  ellipse,  unless 
the  connecting-rod  is  of  infinite  length  in  which  case  the  points  1',  2',  3',  etc.,  would  lie  on  the  ordi- 


36 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


nates  through  d,  c,  b,  etc.  In  Fig.  42  the  dotted  curve  is  for  the  mechanical  equivalent  of  the  infinite 
connecting-rod,  and  is  a  true  ellipse,  while  the  full  curve  is  for  a  connecting-rod  =  4  crank  lengths. 

For  the  crank  position  a  d,  or  the  equivalent  piston  position  e  h,  Fig.  42,  and  the  finite  con- 
necting-rod, the  valve  is  off  center  the  distance  h  e.  If  the  valve  has  a  lap  =  h  f  the  steam-port 
opening  for  this  position  is  /  e  on  the  head  end,  and  if  the  exhaust-lap  on  the  crank  end  of  the  valve 
is  h  g  the  opening  of  the  port  to  exhaust  is  g  e.  The  steam  and  exhaust-lap  lines  are  drawn  parallel 
to  the  center-line  b  c. 

It  follows,  then,  that  the  point  in  which  the  steam-lap  line  intersects  the  valve  ellipse  deter- 
mines directly  the  piston  positions,  and  indirectly  the  crank  positions  at  admission,  cut-off,  etc. 


FIG.  41. 

For  cut-off  on  the  head  end,  finite  card,  the  piston  is  at  I",  directly  below  I,  Fig.  42.  Projecting  I 
to  the  center-line  and  drawing  an  arc  with  the  connecting-rod  as  the  radius,  a  m  is  obtained  for  the 
crank  position  at  cut-off.  In  like  manner  the  crank  positions  for  release,  compression  and  admis- 
sion may  be  found. 

Method  of  Determining  Steam  and  Exhaust-Port  Openings,  and  Steam  and  Exhaust-Laps  bij  Combining 
the  Valve  Ellipse  and  Indicator  Cards,  and  Without  Removing  Steam  Chest  Cover. 

By  combining  the  valve  ellipse  and  the  indicator  card,  as  shown  at  Figs.  42  and  43,  a  ready 
means  is  afforded  for  examining  the  steam  distribution  of  a  plain  D-  or  piston-valve,  and  also  for 
determining  the  steam  and  exhaust  laps,  without  removing  the  steam  chest  cover  or  disturbing  the 
valve  or  the  running  of  the  engine  in  any  way.  This  is  done  by  taking  the  indicator  card  from  the 
engine  in  the  usual  way,  and  at  the  same  time  taking  the  valve  ellipse  .Automatically  from  the 
engine,  and  drawing  the  two  curves  one  under  the  other  as  in  Figs.  42  and  43.  The  full-line  valve 
ellipse  is,  so  far  then,  all  that  is  known  in  Fig.  42.  In  obtaining  the  valve  ellipse  the  abscissae 
displacements  would  come  from  the  cross-head,  and  the  ordinate  displacements  from  the  valve 
stem.  To  get  at  the  information  which  it  contains,  first  draw  the  lines  s  t  and  u  v  tangent  to  the 
ellipse  and  parallel  to  the  stroke  line,  which  would  be  recorded  in  obtaining  the  ellipse  card.  The 
perpendicular  distance  betewen  s  t  and  u  v  is  the  valve-travel.  Draw  the  line  b  c  midway  between 
s  t  and  u  v. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


37 


On  the  indicator  card  determine  the  points  V  (cut-off),  n'  (release),  p'  (compression)  and  q' 
(admission),  and  project  these  points  up  to  the  ellipse  at  I,  n,  p,  and  q.  Then  since  admission  and 
cut-off  are  both  governed  by  the  steam-lap,  the  points  I  and  q  should  each  be  a  distance  from  6  c 
equal  to  the  steam-lap,  and  lie  on  the  steam-lap  line,  which  is  thus  determined.  Likewise  n  and  p 
should  each  be  the  same  distance  from  b  c,  and  determine  the  exhaust-lap. 

The  laps  of  the  valve,  together  with  its  travel,  and  also  the  steam  and  exhaust-port  opening 
at  any  instant,  are  now  known  for  the  head  end.  For  the  crank  end,  the  crank  end  indicator 
card  and  ellipse  would  be  taken  in  the  same  manner. 


Cut-off.  //.£. 


FIG.  42. 


FIG.  43. 


38 


VALVES,   VALVE-GEARS   AND  VALVE  DIAGRAMS 


SINUSOIDAL  DIAGRAM. 


In  this  diagram  the  crank  angles  are  laid  off  on  the  abscissa  line,  and  the  piston  and  valve  dis- 
placements on  the  ordinates. 

The  sinusoidal  diagram  affords  a  ready  means  for  studying  the  steam  distribution  for  setting 
the  eccentric  so  as  to  secure  the  best  results  for  a  given  engine. 

In  Fig.  44  take  a  distance  such  as  b  c  to  represent  360  degrees,  and  divide  the  line  into  a  con- 
venient number  of  equal  parts.  On  the  ordinates  through  the  division  points  lay  off  distances 
equal  to  the  corresponding  piston  displacements,  thus  obtaining  a  curve  through  the  points  c  d  b. 


225°    I8T    /J35°       9O°      45 


FIG.  44. 


For  the  infinite  connecting-rod  the  curve  is  a  sinusoid,  as  shown  by  the  dotted  line.  The  points 
on  the  solid  curve,  which  in  this  case  is  for  a  connecting-rod  equal  to  four  crank  lengths,  are  found 
by  making  the  ordinates  through  45°,  90°,  etc.,  of  Fig.  44,  equal  to  g  d,  f  d,  etc.,  of  Fig.  45,  which 
is  here  drawn  two-thirds  size. 

In  Fig.  44  the  sinusoidal  curve  i  w  j  has  its  maximum  orch'nate  v  w  =  Yi  valve-travel,  and  its 
pitch  x  y  =  b  c.  The  distance  a  s  corresponds  to  an  assumed  angle  of  advance,  which  in  this  case 
is  equal  to  35°.  This  curve,  as  drawn  in  Fig.  44,  neglects  the  angularity  of  the  eccentric-rod,  and 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


39 


is  a  sinusoid.     It  may  be  so  used  practically,  unless  an  investigation  is  one  of  much  precision,  in 
which  case  the  actual  valve  curve  may  be  found  by  the  method  shown  in  Fig.  45. 
In  Fig.  44,  let  b  k   =  the  steam-lap,  head  end. 
bq    =      "        "     "'    crank  end. 
b  o    =      "  exhaust-lap,  head  end. 
b  m  =      "  "  crank  end. 

Draw  lines  through  k,  q,  o  and  m,  parallel  to  b  c.  Then  cut-off,  head  end,  occurs  at  t  (126°), 
release  at/  (158°),  compression  at  g  (315°),  and  admission  at  h  (355°).  The  degrees  here  given 
are  for  illustration,  and  therefore  only  approximately  correct.  I  e  is  the  lead. 


135, 


f 


EM* 


FIG.  45. 


In  order  to  use  this  diagram  for  determining  the  effect  of  different  angles  of  advance,  the  valve 
curve  should  be  extended  as  shown  to  i  and  j,  and  then  drawn  on  a  piece  of  tracing  paper  or  cloth. 
By  placing  the  curve  so  that  s  falls  on  a  the  events  of  the  stroke  for  zero  angle  of  advance  are  found 
at  once;  with  s  at  n  (90°)  the  events  for  90°  angle  of  advance  are  known.  For  intermediate  angles 
of  advance  s  falls  between  a  and  n.  The  effect  of  changing  the  valve  laps  may  also  be  readily 
shown  by  raising  or  lowering  the  lap  lines. 


SECTION   III,— TYPES   OF  VALVES. 
EFFECT  OF  FRICTION  DUE  TO  PRESSURE  ON  BACK  OF  PLAIN  D- VALVE. 

Thus  far  in  these  notes  the  plain  D-valve  and  the  Allen  valve  are  the  only  types' that  have 
been  treated  in  the  classroom  work.  It  has  been  shown  that  the  plain  D-valve  has  a  limited  range 
of  application,  and  that  for  cut-offs  earlier  than  %  stroke  a  D-valve  of.  excessive  and  impracticable 
weight  and  travel  would  be  required.  Furthermore,  the  steam-pressure  on  the  back  of  the  plain 
D-valve,  in  addition  to  the  pressure  due  to  the  weight  of  the  valve  (when  in  a  horizontal  position) , 
increases  largely  the  friction  on  the  valve-seat.  In  an  engine  of  14-in.  bore,  with  a  plain  D-valve 
8^2  ins.  long  and  12J/2  ins.  wide,  and  a  steam  pressure  of  70  Ibs.,  the  pressure  on  the  back  of  the 
valve  would  be  8.5  X  12.5  X  70  =  7437  Ibs.,  or  3.7  tons.  When  a  valve  is  so  designed  that  this 
pressure  cannot  act  on  any  considerable  portion  of  it  so  as  to  produce  pressure  and  friction  on  the 
valve-seat,  it  is  said  to  be  "  balanced."  In  engines  (especially  those  of  high  speed)  where  the 


40 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


adjustment  of  the  cut-off,  etc.,  is  produced  by  the  effort  of  the  governor  in  changing  the  position  of 
the  valve,  the  friction  due  to  such  high  pressure  is  too  great  to  be  properly  overcome  directly. 

CLASSIFICATION  OF  VALVES. 

Other  forms  of  valves  must,  therefore,  be  adopted,  and  these  forms  may  be  roughly  classed  as 
follows,  an  exact  classification  and  a  simple  one  that  would  include  the  numsrous  variations  and 
combinations  of  types  being  practically  impossible : 

One-Piece  Valves. 

1.  Valves  in  which  the  steam  pressure  is  balanced,  permitting  large  travel  if  desired. 

2.  Valves  which  are  double-ported,  and  require  less  travel. 

3.  Valves  which  are  both  balanced  and  double-ported,  including  classes  1  and  2. 

Valves  With  Two  or  More  Parts. 

4.  Valves  which  operate  by  the  motion  of  two  or  more  parts. 

,  Piston-Valve. 

In  the  1st  and  3d  classes  come  most  prominently  the  simple  "piston"  and  the  "pressure-plate" 
types.  A  simple  piston-valve  is'shown  in  Figs.  46  and  47,  which  is  the  style  adopted  in  the  Forbes 
high-speed  engine.  For  purposes  of  computation  in  designing,  the  piston-valve  may  be  considered 
as  an  ordinary  D-valve  with  its  plane  surface,  and  also  the  rectangular  steam-ports,  rolled  into  a  cylin- 
drical form.  In  Figs.  46  and  47,  A  is  the  circular  steam-port  through  the  valve  liner,  or  bushing;  B 


Sect /on    throve/It    Q. 
FIG.  46. 


Section    through    Center. 
FIG.  47. 


FIG.  48. 


FIG.  49.— End  view  of  Fig.  48. 


42 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


is  the  steam-port  in  the  cylinder  casting;  C  is  the  live  steam,  and  D  the  exhaust-steam  opening  in  this 
particular  engine.  Small  portions  of  the  piston  and  the  cylinder  head  are  also  shown. 

In  computing  the  area  of  the  port  A  on  the  inside  surface  of  the  liner,  deductions  must  be  made 
for  the  area  of  the  surfaces  of  the  bridges,  three  of  which  are  shown  in  the  end  section  view,  Fig.  46, 
at 'Ay,  A.;,  An.  It  should  be  noted  also  that  the  rectangular  section  (a  b  X  c  d)  in  the  plane  R  must 
equal  the  calculated  area  of  the  port.  Very  often  the  width  of  A  (f  g)  is  made  equal  to  c  d,  and  the 
depth  of  the  piston-valve  made  accordingly.  In  Fig.  47  ef  represents  the  steam-lap,  and  h  g  the 
exhaust-lap. 

The  principal  advantages  of  the  piston-valve  are:  1st,  that  it  is  balanced;  2d,  that  the  valves 
are  at  the  ends  of  the  cylinder,  giving  short  steam-ports,  and  thus  minimizing  condensation;  3d,  that 
when  used  on  the  high-pressure  cylinders  of  multiple-expansion  engines,  steam  may  be  admitted 
from  the  inside,  or  center,  and  exhausted  on  the  outside  of  the  valve,  thus  keeping  the  high  pressure 
and  temperature  of  the  live  steam  away  from  the  stuffing-box.  When  so  used  D,  Fig.  47,  would 
become  the  live  steam,  and  C  the  exhaust-steam  openings;  h  g  would  be  the  steam-lap,  and  ef  the 
exhaust-lap. 

A  disadvantage  arises  from  the  fact  that  if  the  valve  is  a  loose  enough  fit  to  slide  easily,  it  is 
likely  to  allow  the  live  steam  to  leak  through.  In  small  engines  generally  the  piston-valve  is  solid, 
as  in  Figs.  46  and  47,  and  a  tight,  sliding  fit,  with  due  allowance  for  expansion  of  valve  and  valve-seat 
due  to  different  temperatures — especially  in  starting — must  be  relied  upon  to  prevent  leakage. 

When  spring  packing-rings  are  used  on  a  piston-valve  they  must  necessarily  be  thin,  and  have  a 
small  pressure  on  the  valve-seat  to  avoid  excessive  friction  and  wear,  and  they  are  liable  to  break. 
Adjustable  packing-rings  must  be  carefully  handled,  or  they  will  bind  and  strip  the  valve-gear. 
When  spring  or  adjustable  packing-rings  are  used  the  steam  and  exhaust  laps  are  measured  from 
the  edges  of  the  ring,  or  rings,  to  the  edges  of  the  port,  instead  of  from  the  edges  of  the  valve  casting.  A 
piston- valve  with  adjustable  rings  is  shown  in  Figs.  48  and  49.  It  is  one  of  the  typss  used  on  the 
"Ideal"  engine.  The  adjustable  rings  A  and  A'  are  turned  accurately  to  the  bore  of  the  bushing 
and  then  split  across  to  permit  of  expansion  when  the  head,  B,  B',  is  turned,  so  that  the  cam  surfaces 
between  B  and  C  press  radially  on  the  shoes  E,  and  these  in  turn  on  the  rings  A .  Holes  for  a  spanner 
wrench  are  drilled  in  B,  but  are  omitted  in  the  illustration. 

Piston-valves  may  be  single  or  double-ported,  the  same  as  flat  valves.     Fig.  51  shows  the  Arm- 


FIG.  50. 


FIG.  51. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


43 


ington  &  Sims  type  of  piston-valve  with  double  admission  ports  similar  to  the  Allen  valve.  It  will  be 
noted  in  Fig.  51  how  the  steam-chest  walls  at  a  and  b  are  cored  to  facilitate  uniform  heating  and  cool- 
ing of  the  valve,  valve  bushing,  and  adjacent  steam-chest  wall. 

Fig.  52  shows  a  single  piston-valve  controlling  both  the  high-  and  low-pressure  pistons  of  a  com- 
pound engine  as  applied  to  the  Vauclain  compound  locomotive  manufactured  at  the  Baldwin  Loco- 
motive Works,  Philadelphia,  Pa.    Both  pistons 
move  in  the  same  direction  at  the  same  time 


and  are  secured,  through  their  rods,  to  the 
same  cross-head.  Live  steam  enters  the  steam 
chest  at  A,  A,  and  passes,  at  the  phase  shown 
in  the  illustration,  through  the  head-end  port 
to  the  high-pressure  cylinder.  The  exhaust 
steam  from  the  high-pressure  cylinder  is  flow- 
ing in  the  direction  of  the  arrows  through  the 
hollow  center,  B,  of  the  piston-valve  body  to 
the  head  end  of  the  low-pressure  cylinder. 
The  exhaust  from  the  low-pressure  cylinder 
passes  out  through  the  exhaust  port,  C,  to  the 
smoke  stack.  For  the  sake  of  clearness,  this 
illustration  is  distorted  to  the  extent  that  the 
center-line  of  the  steam  chest  and  valve  is 
shown  in  the  plane  of  the  two  cylinder  center- 
lines,  whereas,  to  save  space  in  locomotive 
construction,  it  is  placed  back  of  this  plane. 
It  will  be  noted  that  the  valve  is  really  two 
piston-valves  combined,  one  formed  by  the 
outer  rings  marked  D  D,  controlling  the  high 
pressure  and  the  other  formed  by  the  inner 
rings  marked  E  E,  controlling  the  low-pressure 
cylinder. 


FIG.  52. 


Another  type  of  piston-valve,  with  double- 
ports  and  adjustable  packing-ring,  as  used  on 

the  Fitchburg  engine,  is  shown  in  Fig.  53.  Four  of  these  valves  are  used  on%he  engine,  the  two  live- 
steam  valves  being  operated  by  a  cam-wrist  plate  and  regulator  automatically  controlling  the  cut-off, 
and  the  two  exhaust  valves  from  a  separate  eccentric.  The  live-steam  valve  for  the  head-end  port 
is  shown  in  the  illustration.  The  action  of  the  valve  and  method  of  adjustment  will  be  apparent  on 
inspecting  the  drawing,  it  being  specially  pointed  out  that  the  cone,  6,  has  a  small  clearance  at  the 
right-hand  end  and  may  be  adjusted  and  locked  in  any  position  by  releasing  the  tension  bolts,  d  d,  and 
tightening  the  compression  bolts,  e  e,  against  the  lugs  c  of  the  cone.  The  expansible  ring,  .a,  a,  a,  a, 
with  its  parts  joined  by  radial  ribs  (not  shown),  is  split  on  a  line  parallel  with  the  piston  rod  and 
junction  strips  are  set  crosswise  to  keep  the  steam  from  passing  through. 

Pressure-Plate  Valves. 

The  pressure-plate  type  of  balanced  valve  may  be  shown  by  the  valve  used  on  the  "Straight 
Line"  engine  designed  by  Prof.  Sweet,  in  Fig.  54.     A  A  is  the  pressure-plate  which  receives  the 


44 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


pressure  of  the  steam.  It  is  prevented  from  pressing  on  the  valve  by  " distance-blocks"  (not 
shown),  slightly  thicker  than  the  valve  which  slides  between  the  seat  and  the  plate,  and  is  thus 
relieved  of  all  pressure.  The  distance  blocks  are  exposed  to  live  steam  the  same  as  the  valve  in 
order  to  prevent  binding  of  the  valve  between  the  pressure-plate  and  seat  by  expansion,  especially 


FIG.  53. 

when  starting  up.  The  valve  is  shown  open  to  lead  on  the  left  end.  It  is  double-ported.  The 
projections  at  6  b  are  for  protecting  the  finished  surface  of  the  pressure-plate  from  the  cutting 
action  of  the  exhaust  steam. 

The  system  of  balancing  valves  by  pressure-plates  is  more  completely  shown  in  Figs.  55-57, 
which  represent  three  types  of  balanced  or  pressure-plate  valve — the  fixed,  the  adjustable  and  the 
flexible. 

In  Fig.  55,  steam  is  prevented  from  acting  on  the  top  of  the  valve  by  the  bars  a,  b,  etc.,  of  which 
there  are  four,  pressing  against  the  fixed  plate  c  by  means  of  springs  in  the  bottom  of  the  grooves 
which  hold  the  bars. 


FIG.  54. 

In  Fig.  56,  steam  is  prevented  from  acting  on  the  top  of  the  valve  by  means  of  the  adjustable 
pressure-plate  shown  in  the  background  at  b  c  e  f,  which  is  bounded  on  the  top  by  the  incline 
plane  6  c  and  moved  or  adjusted  by  the  rod  a.  This  incidentally  shows  a  type  of  double-ported 
valve,  similar  to  the  Allen  valve,  there  being  a  cored  passageway  (not  shown,  except  as  indicated 
by  arrows)  from  one  side  of  the  valve  to  the  other. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


45 


In  Fig.  57,  steam  is  prevented  from  acting  on  the  top  of  the  valve  by  means  of  the  flexible  plate, 
a,  of  steel  or  other  elastic  metal  so  designed  as  to  allow  the  steam  pressure  in  the  steam  chest  to 
force  the  bands  d  and  e  down  on  the  top  of  the  valve  with  only  sufficient  pressure  to  prevent  leak- 
age. 

In  the  fixed  type  of  pressure-plate  valve,  live  steam  is  sometimes  relied  upon  to  supply  the 
pressure  exerted  by  the  springs  as  described  in  connection  with  Fig.  55,  the  live  steam  being  admitted 
through  small  openings  bored  in  the  body  of  the  valve  to  the  under  side  of  the  bars.     The  bars 
themselves  are  sometimes  enlarged  upon  and 
developed  to  such  an  extent  as  to  be  unrecog- 
nizable as  bars,  they  having  cut-off  and 
edges  and  controlling  the  steam  the 
the  original  part  of  the  valve.     Such  types  are 
shown  in  Figs.  58   and  59,  the  former  being 
known   as   the   Ball   telescopic    valve,   manu- 
factured by  the  American  Engine  Co.,  Bound 
Brook,  N.  J.,  and  the  latter  as  the  flat  balanced 
expanding  valve  manufactured  by  the  Skinner 
Engine  Co.,  Erie,  Pa. 

The  Ball  valve  has  two  rectangular  faces  and  a  cylindrical  body,  the  live  steam  being  admitted 
through  the  inside,  and  the  exhaust  steam  passing  around  the  outside  edges.  The  valve  seats  in 
the  steam  chest  in  this  design  lie  in  planes  perpendicular  to  the  steam-chest  ,cover  plate,  these 
necessitating  tortuous  steam-ports.  This  very  construction,  however,  gives  double  steam  admis- 
sion and  exhaust  ports  and  makes  the  valve  in  reality  a  "double-ported"  valve  with  its  small  valve- 
travel  and  without  the  extra"  passageway  in  the  valve.  The  flat  balanced  valve  shown  in  Fig. 


FIG.  55. — Fixed  type  of  pressure-plate  valve. 


FIG.  56. — Adjustable  type  of  pressure-plate  valve. 

59  is  entirely  rectangular  and  made  in  two  parts  with  alternate  rectangular  bars  and  grooves  cut 
parallel  to  the  port  and  nearly  across  the  entire  width  of  the  valve.  The  depth  of  the  grooves  is 
a  little  greater  than  the  height  of  the  bars  so  that  when  fitted  together  there  is  room  for  the  live 
steam  to  flow  in.  The  pressure  thus  exerted  at  the  twelve  spaces  similar  to  the  three  shown  in  the 
upper  left  half  of  the  Figure  at  d,  forces  one-half  of  the  valve  against  the  valve-seat  and  the  other 
half  against  the  face  of  the  steam-chest  cover.  In  the  position  shown,  the  first  space,  counting  from 


46 

either  side,  exercises  the  balancing  pressure.  As  soon  as  the  valve  opens  to  live  steam,  spaces  two 
and  three  receive  full  balancing  pressure.  When  the  valve  closes  for  compression  the  fourth  and 
fifth  spaces  are  subjected  to  compression  pressure.  The  sixth  space  always  has  the  same  pressure  as 


^^ 


FIG.  57. — Flexible  type  of  pressure-plate  valve. 

the  exhaust.     The  end  areas  of  the  valve  are  so  proportioned  that  the  live  steam  pressure  keeps  the 
two  parts  of  the  valve  steam  tight  at  e.     The  valve  is  double-ported,  bothf  for  live  and  exhaust 


FIG.  58. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


47 


steam.  The  spring  at  the  center  of  the  valve  is.  designed  to  hold  the  two  parts  in  correct  initial 
position  before  steam  pressure  is  applied.  The  part  of  the  valve  marked  with  the  letters  g  and  /,  is 
an  L-shaped  hook  in  which  the  end  of  the  valve  stem  engages. 

Double-Ported  Valves  or  Their  Equivalent. 

Prominent  examples  of  the  second  class  of  valves  are  the  Allen  valve  arid  the  Double-Ported 
valve.  The  Allen  valve,  as  used  in  American  locomotive  practice,  is  balanced  as  shown  in  dotted 
lines  in  Fig.  32  of  these  notes.  The  double-ported  valve  is  usually  balanced.  Numerous  types 


FIG.  59. 

of  valves  have  provision  for  admitting  steam  to  the  main  port  through  more  than  one  aperture  in 
the  valve,  as  shown  in  illustrations  already  given  in  the  piston  and  pressure-plate  types. 

From  what  has  preceded,  it  appears  that  many  valves  of  the  third  class  have  the  combined 
features  of  those  of  the  first  and  second  classes. 

Valves  Which  Operate  by  Two  or  More  Independent  Parts. 

In  valves  of  the  fourth  class  we  will  take  up: 

First,  valves  divided  into  two  parts  known  as  "double  valves." 

Second,  valves  divided  into  four  parts. 

Third,  valves  combining  the  features  of  the  first  and  second  classes  just  mentioned. 

Two-Part  Valves. 

In  the  first  class,  or  in  the  double  valves,  there  are  three  distinct  types,  viz:  the  Gonzenbach, 
Polonceau,  and  Meyer,  shown  in  Figs.  60,  62,  and  63,  respectively.  In  each  of  these  three  designs 
the  lower  valve,  or  one  nearest  the  cylinder,  is  called  the  "main"  or  "distribution  valve."  The 
upper  valve  is  called  the  "auxiliary"  or  "cut-off  valve."  The  passageways  through  the  seat 
in  Fig.  60,  and  through  the  main  valves  in  Figs.  62  and  63,  are  called  the  "auxiliary  ports."  The 
two  parts  of  the  complete  valve  are  operated  by  independent  gears. 

The  advantage  of  valves  of  this  type  is  that  the  cut-off  may  be  varied  independently  of  the 
other  events  of  the  stroke,  for  the  reason  that  the  auxiliary  valve  affects  only  the  cut-off,  while  the 
main  valve  governs  the  admission,  release  and  compression. 


48 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


Gonzenbach  Valve.  The  Gonzenbach  valve  has  two  separate  steam  chests,  A  and  B,  Fig.  60. 
The  partition  C  has  a  rectangular,  port-shaped  opening  D.  The  Zeuner  diagram  for  this  valve  may 
be  constructed  as  follows:  In  Fig.  61  let  E  F'  0  F  and  G  0  G'  be  the  Zeuner  circles,  and  0  F  and 
O  G  the  outside  laps  of  the  main  valve.  The  exhaust  construction  for  this  type  of  valve  is  treated 
entirely  in  the  same  way  as  in  the  diagram  for  the  plain  D-valve,  and  is  therefore  omitted  here. 
The  angle  of  advance  for  the  main  valve  may  be  assumed  to  be  8. 

LetO  H  be  the  half-travel,  w  the  angle  of  advance,  which  is  negative  (subtracted  from  90°), 
for  the  auxiliary  part  in  this  type  of  valve,  and  H  K  0  L  the  Zeuner  circle  for  the  auxiliary  valve. 

Then  for  the  crank  position  0  I  the  main  valve  is  off  center  a  distance  =  0  J,  and  the  auxiliary 
valve  is  off  center  a  distance  =  0  K.  In  Fig.  60  it  may  be  seen  that  when  the  left-hand  edge  of 


FIG.  60. 

the  opening  E  reaches  the  right-hand  edge  of  the  opening  D,  the  main  steam  chest  B  is  closed,  and 
live  steam  is  cut  off  from  the  cylinder  even  if  the  main  port  F  is  still  open.  When  the  opening 
of  the  port  D  becomes  zero,  the  auxiliary  valve  is  off  center  a  distance  =  Y^  E  +  y%  D ;  this  dis- 
tance is  usually  designated  byS,  and  is  represented  in  Fig.  61  by  the  radius  0  L  of  the  arc  L  M. 
Then  the  auxiliary  valve  covers  the  passage-way  D  while  the  crank  is  going  from  0  N  to  0  P,  and 
opens  it  at  0  P  just  before  the  main  valve  opens  the  main  port  at  the  crank  position  0  Q  on  the 
return  stroke. 

In  this  type  of  valve,  then,  the  opening  of  the  auxiliary  port  must  always  occur  after  the  main 
port  closes  on  one  end  (closes  atOFR),  and  before  it  opens  on  the  other  (opens  at  0  G  Q).  There- 
fore 0  P  must  always  come  between  the  crank  positions  0  R  and  0  Q.  If  Y^  E  +  }/%  D  is  made 
equal  to  0  H,  0  P  will  fall  on  0  R  and  the  cut-off  and  main  valves  will  both  close  at  the  same  time. 
In  this  case  the  half  valve-travel  of  the  auxiliary  is  just  equal  to  Y^  E  +  }/%  D  and  the  auxiliary 
port  will  be  closed  for  an  instant  only.  H  Y2  E  +  l/2D  =  0  T,  OP  will  fall  on  0  Q,  and  auxil- 
iary cut-off  will  take  place  at  0  I,  and  the  auxiliary  port  will  be  closed  while  the  crank  is  burning 
from  0  I  to  0  Q.  The  cut-off  therefore  is  limited  between  the  crank  positions  0  I  and  0  R,  and 
S  may  have  any  value  between  0  K  and  0  H. 

Should  a  valve-gear,  constructed  so  that  Y^E  +  %  D  =  0  V ',  have  its  angle  of  advance  reduced 
from  o)  to  zero,  auxiliary  cut-off  would  take  place  earlier  at  0  W,  and  auxiliary  port-opening  would 
occur  at  0  F,  before  the  main  port  had  closed  at  0  R.  Therefore  steam  would  be  admitted  twice 
on  one  stroke,  illustrating  the  inadvisability  of  altering  angle  of  advance  without  previously  deter- 
mining, by  means  of  a  valve  diagram,  what  the  effect  would  be. 

In  laying  out  a  valve  of  this  kind  the  area  of  the  main  port  F,  Fig.  60,  should  be  calculated  the 


VALVES.   VALVE-GEARS  AND  VALVE  DIAGRAMS 


49 


same  as  in  the  plain  D-valve;  the  area  of  the  auxiliary  port  D  (or  ports,  as  there  are  sometimes 
two  or  more)  should  be  made  slightly  larger  than  the  area  of  the  steam-port  opening  and  the  area 
of  the  opening  at  E  in  the  cut-off  valve,  or  block,  should  be  slightly  greater  than  at  D  depending 


\ 


FIG.  61. 


on  the  desired  range  of  cut-off,  etc.,  as  found  from  the  Zeuner  diagram.  The  point  G  of  the  cut- 
off valve  may  be  located  a  distance  from  the  right-hand  edge  of  D  =  Y^  travel  of  valve  +  ^  inch, 
so  that  G  will  never  overtravel  the  port  and  allow  steam  to  enter  at  the  wrong  time. 


FIG.  62. 


50  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

In  the  Polonceau  and  Meyer  valves  the  auxiliary  parts  slide  on  the  top  of  the  main  block,  and 
both  are  inclosed  in  the  same  steam-chest. 

Polonceau  Valve.  This  valve  is  made  in  two  parts,  A  and  B,  as  shown  in  Fig.  62.  The  main 
part  A  is  laid  out  as  an  ordinary  D-valve.  The  cut-off  block  B  is  solid  and  slides  on  A.  The 
motion  of  B  is  designed  so  that  it  will  close  the  passageway  C  at  any  desired  point  after  C  has  opened 
to  E.  The  angular  advance  of  the  auxiliary  block  is  made  large,  in  some  cases  as  much  as  90°. 
Then  for  half  cut-off  the  eccentric  (180°  ahead  of  the  crank)  is  moving  with  its  maximum  velocity. 
Inasmuch  as  the  use  of  this  valve  is  limited  by  its  range  of  cut-off,  it  is  not  necessary  to  follow 
through  the  diagram,  as  its  application  contains  nothing  that  is  not  given  in  the  Gonzenbach  or 
Meyer  diagrams.  The  former  has  been  explained,  and  the  latter  will  be  in  the  further  notes  accom- 
panying the  problem  to  be  constructed  in  the  drafting  room. 

Regarding  the  dimensions  of  this  valve,  it  should  be  noted  that  the  passageways  C  and  D  should 
be  slightly  larger  than  the  ports  E  and  F  to  allow  for  friction  of  flow  of  steam.  The  length yof  the 
block  B  should  be  such  that  its  left-hand  edge  never  passes  the  left-hand  edge  of  D.  Therefore, 
length  of  B  =  greatest  distance  two  blocks  ever  get  apart  —  (S  —  width  of  D)  +  %  inch.  In 
order  to  obtain  smooth  wear  the  edges  of  B  must  overtravel  the  edges  of  A . 

Meyer  Valve.  In  the  Meyer  valve  the  main  part  is  designed  in  a  manner  similar  to  that  of  the 
plain  D-valve,  while  the  cut-off  device  consists  of  two  blocks,  as  shown  in  Fig.  63.  These  blocks 
are  adjustable  through  a  right  and  left  screw  while  the  engine  is  in  motion.  Thus  the  point  of 
cut-off  may  be  made  to  occur  at  any  point  in  the  stroke  up  to  cut-off  by  the  main  valve,  which  is 
designed  to  take  place  near  the  end  of  the  stroke.  The  notes  for  drafting  table  problem  4,  which 
consists  in  laying  out  a  complete  design  from  assigned  data,  give  a  full  explanation  of  the  working 
of  the  valve  and  of  the  laying  out  of  the  valve  diagram,  which  requires  additional  construction 
work  not  met  with  in  previous  problems. 

A  very  exhaustive  treatise  on  the  subject  of  double  valves  may  be  found  in  Zeuner's  "Treatise 
on  Valve-Gears,"  pages  159  to  219. 

DRAFTING  TABLE  PROBLEM,  No.  3. — DOUBLE-PORTED  VALVE. 

To  design  a  double-ported  valve  for  the  low  pressure  cylinder  of  the  series  of  U.  S.  Battleships  Nos.  13  to  17  ("Vir- 
ginia," "Nebraska,"  "Georgia,"  "New  Jersey,"  and  "Rhode  Island"). 

Bore  =  66  inches.     Stroke  =  48  inches.     Revolutions  =  120. 
Cut-off  for  top,  or  head  end,  =  0.784  of  stroke. 

"     "    "  bottom  =  0.715  "       " 

Length  of  ports  =  62  finches. 
Exhaust  release  for  top,  or  head  end,  «=  3ff  inches. 
"  ">       "bottom  -  5A inches. 

Velocity  of  entering  steam  =  175.1  feet  per  second. 

"exhaust        "     -  125        "     " 
Steam  lead,  top,  =  $i  inch  for  each  half  of  port. 

Length  of  connecting-rod  =  96  inches.     Width  of  bridge  =  2  inches. 
Diameter  of  valve-rod  through  valve  =  2-fg  inches. 

Method  of  .Computation  When  More  Than  One  Port  is  Used. 

For  the  double-ported  valve  each  steam-port  in  the  valve-seat  is  divided  into  two  parts  (m  n 
and  s  t,  Fig.  64,  for  port  T),  so  that  each  part  supplies  a  port  passage  with  one-half  the  total  amount 
of  steam  flowing  into  the  cylinder.  The  exhaust  port  Q  is  made  single,  being  the  same  as  for  a 
plain  D-valve.  The  arrangement  of  the  ports  and  passages  is  shown  in  Fig.  64. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


51 


As  in  the  Allen  valve,  only  one-half  the  steam-port  opening  need  be  taken  into  account  in  con- 
structing the  valve  diagram,  since  the  inner  port,  which  gives  the  other  half  of  the  full  port-opening, 
is  uncovered  at  the  same  time  that  the  outside  port  is  opened. 

Calculate  the  area  of  the  steam-port  opening  for  one  end  of  the  cylinder,  considering  the  veloc- 
ity of  the  inflowing  steam  as  given  in  the  data  for  the  problem.  (In  triple-expansion  marine  work 
it  is  common  to  assume  the  steam  velocity  for  low  pressure  cylinder  from  6000  to  12,000  feet  per 
minute).  Take  one-half  of  this  area  as  the  required  area  to  be  opened  at  each  port.  Divide  this 
by  the  net  length  of  the  ports  to  obtain  the  amount  which  the  valve  is  to  uncover  the  ports  for 
inlet  steam.  With  this  port-opening,  the  proper  lead,  and  the  cut-off,  construct  the  Zeuner  diagram. 
The  result  will  be  a  valve  having  half  the  travel  of  that  of  the  plain  D-valve  with  the  same  effective 
opening,  lead,  and  point  of  cut-off. 

In  this  respect  the  Allen  valve  has  the  same  advantage  as  the  double-ported  valve,  but  the 
Allen  valve  can  only  be  used  with  a  direct  connected  eccentric  when  the  points  of  cut-off  are  earlier 


FIG.  63. 

than  ££  stroke;  the  double-ported  may  be  designed  for  a  broader  range  of  cut-off,  but  it  has, 
however,  a  greater  area  on  which  the  unbalanced  steam  pressure  can  act.  This  disadvantage 
may  be  overcome  by  balancing  the  valve  as  shown  in  Figs.  64  and  65  by  packing-rings  (as,  for 
example,  at  E),  which  are  kept  firmly  against  the  steam-chest  cover  H,  by  means  of  springs,  thus 
excluding  steam  pressure  from  the  space  G.  After  the  Zeuner  diagram  is  completed  for  both  ends, 
the  various  dimensions  for  the  valve  are  found  by  the  following  rules,  most  of  which  may  be  veri- 
fied by  tracing  the  valve-seat  J,  Fig.  64,  on  the  edge  of  a  piece  of  paper  and  moving  the  paper  the 
amount  of  the  valve-travel: 

The  minimum  width  of  bridge  (k  I  and  i  j)  must  be  such  that,  for  example,  the  point  g  of  the 
valve  will  not  under  any  circumstances  come  closer  than  %"  lto  j  of  the  valve-seat.  It  may  be 
found  by  the  following  formula: 

Minimum  steam-lap  +  port  width  +  minimum  bridge  width  =  half  valve-travel  -f-  }£' . 

If  the  result  should  be  a  negative  quantity,  or  less  than  the  thickness  of  the  cylinder  wall  (in 
this  problem,  2  inches)  discard  it,  and  make  the  bridge  width  equal  to  the  cylinder  wall  thickness 
to  help  insure  a  sound  casting. 

Find  the  width  of  the  exhaust  port  j  k  which  must  be  such  that  when  the  valve  is  in  its  extreme 
position  there  shall  be  an  opening  at  least  equal  to  the  total  steam-port  width  for  one  side  of  the 
cylinder.  This  may  be  found  by  the  following  formula: 

Width  of  exhaust  port  =  ^  travel  of  the  valve  +  maximum  exhaust  lap  +  total  width  of 
steam-ports  for  one  end  —  width  of  bridge. 


52 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


/  g  =  steam-port  opening  head  end;  and  o  p  =  steam-port  opening  crank  end. 

The  thickness  p  q  or  e  f,  Fig.  64,  depends  entirely  on  practical  considerations.  It  is  a  part  of 
the  partition  wall,  and  must  be  thick  enough  to  give  a  good  casting,  and  to  allow  facing.  In  the 
present  design  make  it  \Yi  inches. 

The  length  of  that  part  of  the  valve-seat  (n  s  and  d  h,  Fig.  64)  between  the  two  inlet  ports  on 


Section  through  c-e/iter. 


Section  through  CD. 


FIG.  64. 


Section  through  A B 


Section  through  center. 


FIG.  65. 


each  end  must  be  such  that  the  point  q  does  not  overtravel  s.  The  proper  length  is  determined 
by  the  following  formula : 

Steam-lap  -f  opening  of  port  +  p  q  +  Yi  travel  of  valve. 

The  width  of  the  exhaust  passage  d  e  and  q  r-  through  the  valve,  Fig.  64,  will,  according  to  the 
previous  paragraph,  be  equal  to  Yi  travel  minus"  exhaust- lap  (according  to  end  for  which  compu- 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  53 

tation  is  being  made) .  Should  this  give  values  to  d  e  or  q  r  less  than  c  d,  it  will  be  necessary  to 
arbitrarily  lengthen  n  s  and  d  h.  This  can  only  happen  when  port  width  plus  exhaust-lap  is  greater 
than  half  valve-travel  and  will  rarely,  if  ever,  occur. 

The  ports  s  t,  m  n,  h  i,  and  c  d  are  made  equal. 

The  maximum  distance  for  a  c  or  t  v  should  equal  such  an  amount  that  the  points  6  or  u  will 
overtravel  the  edge,  but  not  so  small  that  the  points  d  or  r  will  overtravel. 

Computation  for  Steam  Passageway  in  the  Valve  Itself. 

The  steam  supplied  to  the  inner  steam-ports  /  g  and  o  p  of  the  valve  is  conducted  through 
conical  pipes  from  the  sides  of  the  valve  which  are  shown  at  K  K  in  Figs.  64  and  65.  The  usual 
form  of  a  cross-section  of  these  pipes  is  shown  in  Fig.  64.  The  area  of  a  cross-section  of  the  pipe 
at  y  w  equals  the  area  of  the  steam-port  opening  from  w  to  x,  less  the  area  of  two  supporting  ribs 
S  S,  w  and  y  being  located  by  trial  and  error  to  satisfy  this  condition.  With  the  point  y  deter- 
mined, the  slanting  lines  of  the  top  of  the  pipe  might  be  drawn  directly  to  x,  as  the  left-hand  pipe 
is  not  required  to  feed  the  right  half  of  the  port.  It  is  often  drawn  from  y  tangent  to  the  valve- 
stem  casing,  as  shown  in  Fig.  65.  Make  the  slope  of  the  side  of  the  valve  about  45°. 

The  right  half  of  Fig.  65  shows  a  section  through  the  valve  at  the  center,  and  the  left  half  a 
section  at  A  B  through  one  of  the  "conical  steam  passageways"  or  "pipes,"  as  they  are  called. 

It  now  remains  to  make  the  sum  of  the  two  upper  areas  L  L  in  Fig.  65  equal  to  the  area  of  one 
of  the  steam-ports  at  one  end  of  the  cylinder.  This  is  equal  to  c  d  X  length  of  port.  This  is  most 
easily  accomplished  by  considering  the  areas  as  made  up  of  approximate  triangles. 

Make  out  a  table  as  follows,  and  enter  the  results  of  the  calculations  therein : 

Top,  or  Bottom,  or 

head  end.         crank  end. 

Eccentricity 

Travel  of  valve 

Width  of  port 

Steam-lap 

Exhaust-lap 

Angular  advance 

Steam  lead 

Cut-off,  inches 

Cut-off,  per  cent,  of  stroke 

Exhaust  release  in  inches 

Exhaust  release,  per  cent,  of  stroke 

Compression,  inches 

Steam  opening 

Exhaust  opening* 

Velocity  of  steam,  feet  per  second 

Velocity  of  exhaust  steam,  feet  per  second 

Area  of  Exhaust  Passageway  in  Cylinder. 

The  drawing  is  to  be  completed  as  shown  in  Figs.  64  and  65.     Place  the  Zeuner  diagram  and 
table  of  results  on  one  sheet,  and  the  valve  drawings  on  another.     The  principal  dimensions  for 
*  Enter  the  words  "full  port"  unless  the  exhaust  opening  is  less  than  the  width  of  the  port. 


54  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

such  parts  as  are  not  calculated  will  be  found  on  the  sketch.  The  openings  o  o  are  merely  cored 
out  to  save  weight,  and  have  nothing  to  do  with  the  working  of  the  valve.  In  many  cases  this 
part  of  the  valve-seat  is  cast  solid.  The  area  of  the  exhaust  port  Q,  in  this  case,  is  made  less  than 
the  area  of  the  combined  steam-ports  of  one  end,  allowance  being  made  for  the  fact  that  the  sec- 
tion is  customarily  shown  in  a  central  plane,  and  therefore  only  about  half  of  the  exhaust  steam 
has  to  pass  through  the  section.  In  this  case  the  area  Q  is  about  0.7  of  the  area  of  the  ports.  Imme- 
diately beyond  the  section  Q  the  exhaust  passageway  enlarges,  due  to  the  curvature  of  the  cylin- 
der wall,  and  is  ample  to  conduct  the  steam  to  the  exhaust  pipe,  represented  by.  the  dotted  circle 
with  a  1234-inch  radius. 

In  Fig.  65  the  length  of  the  port  is  shown  as  67^  inches  instead  of  62^  inches  as  given  in  data- 
This  increase  is  made  necessary  by  the  four  IJ^-inch  supporting  ribs  shown  at  S. 

DRAFTING  TABLE  PROBLEM,  No.  4. — MEYER  VALVE. 

In  the  Meyer  valve  the  upper  or  auxiliary  part  is  made  in  two  pieces,  as  indicated  in  Fig.  68 
by  R  and  P,  and  the  cut-off  may  be  varied  at  will  while  the  engine  is  in  motion  by  moving  the  two 
pieces  nearer  together,  or  farther  apart,  by  means  of  the  hand-wheel  0,  shown  in  Fig.  68.  The 
top  view  of  the  main  valve,  which  in  this  case  is  divided  into  two  portions,  is  shown  in  Fig.  67. 

The  present  problem  consists  in  designing  a  Meyer  valve  for  a  steam  air  compressor  of  the 
following  dimensions: 

Stroke • 30  inches 

Bore 16.5  inches 

Revolutions  per  minute 60 

Maximum  cut-off  of  main  valve  (head  end) 

Lead  of  main  valve  (each  end) 0 

Inside  lap  (each  end) 0 

Velocity  of  live  steam 6000  feet  per  minute 

"  exhaust  steam ...  4000   "      " 

Length  of  port 13.5  inches 

Connecting-rod 5  crank  lengths 

Range  of  cut-off  for  auxiliary  valve 

In  the  solution  of  the  problem,  find  first  the  maximum  port-opening  required,  and  then,  by 
means  of  an  ordinary  Zeuner  diagram,  find  the  outside  lap  of  a  plain  D-valve  that  will  give  the 
desired  maximum  cut-off. 

As  shown  in  Fig.  68,  the  live  steam  must  pass  through  the  opening  tube;  hence  b  c  will  be 
equal  to  the  port-opening,  and  inasmuch  as  the  two  parts  of  the  valve  are  not  shown  on  center 
the  steam-lap  will  not  show  directly  but  will  be  equal  to  c  v  -  B  F.  In  the  drawing,  the  valves 
are  shown  in  a  proper  working  position  for  cut-off,  approximately  at  half  stroke  (at  C  F,,  Fig. 
66).  The  scale  of  the  Zeuner  diagram,  Fig.  66,  is  between  four  and  five  times  the  scale  of  Fig.  68. 
The  exhaust  cavity  of  the  valve  is  sometimes  divided  into  two  parts  as  shown. 

To  Find  the  Auxiliary  Valve  Circles  C  K  and  C  L. 

Place  the  cut-off  valve  eccentric  about  45°  in  advance  of  the  main-valve  eccentric. 
Make  the  travel  of  the  auxiliary  valve  in  this  problem  3  inches.     (The  travel  of  the  auxiliary 
valve  in  Fig.  66  is  represented  by  L  K.) 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


55 


To  Find  the  Relative  Valve  Circle  Showing  How  Far  the  Two  Valves  are  Apart  at  any  Instant. 

Draw  the  line  0  K  joining  the  extremities  of  the  diameters  of  the  Zeuner  circles  for  the  main 
and  auxiliary  valves.  Through  the  center  of  the  diagram,  C,  draw  a  line  C  G  parallel  and  equal 
to  0  K.  Upon  this  line  as  a  diameter  describe  a  circle  C  B  H  I  passing  through  the  center.  This 


K 


•r    \ 


7V- 


N 


M 


77 


f\\ 


FIG.  66. 

is  called  the  "Relative  Valve  Circle,"  and  shows  for  any  position  of  the  crank  the  amount  the  two 
valves  are  apart,  as  the  following  example  will  show: 

Suppose  the  crank  at  C  N.  Then  the  main  valve  is  off  center  the  distance  C  M ,  and  still  going 
farther  away;  the  auxiliary  or  cut-off  valve  is  off  center  the  distance  C  N,  and  also  going  farther 
away. 

Hence  the  centers  of  the  two  valves  must  be  the  distance  M  N  from  each  other.  But  if  the 
relative  valve  circle  C  B  H  I  shows  the  relative  positions  of  the  two  valves  for  any  crank  position, 
then  the  distance  C  I  should  equal  M  N,  which  it  does.  This  may  be  shown  by  the  similar  tri- 
angles 0  K  J  and  G  C  I,  the  line  J  K  being  drawn  parallel  and  equal  to  M  N.  A  similar  relative 
valve  circle,  C  F  D,  may  be  used  for  the  analysis  of  the  stroke  on  the  opposite  end  of  the  cylinder. 


56 


VALVES,   VALVE-GEARS  AND   VALVE  DIAGRAMS 


Explanation  of  the  Value  of  S  Which  Determines  the  Point  of  Cut-Off. 

Let  S  =  the  distance  from  the  opposite  edge  of  the  block  (a'  kr,  Fig.  68)  to  the  cutting-off 
edge  of  the  main  valve  (t  6)  when  the  two  valves  are  central  with  respect  to  each  other,  or  S  = 


^_ 

LJ 

r 

1 

1i 

" 

'  !  !' 
V  ^  Jl 

r                  ^ 
i                      i       ' 
i                      i       i 
i                      i       i 
k_                   J      J 

1  1  -  1, 

l_  .  -1  -  —  4  -I 

\                      i       i 

-  -t                                      -4-        —  i  — 

n 

1  1  1, 

n 

1 

!                 i      ' 

z 

1  1  1 
1  1  (<_ 

H~ 

-1-  1  -  11  — 

11  -Jl 

1 

1                                                                 _„!.             _J 

r  r~  -> 

i  i  t1 

r               ^    ^ 
1                   !       ' 

X 

i  i  it 
i  i  1  1 
i  v_  J\ 

Y 

i                   !       i 

v.              .  j       i 

i  j 

i                           i 

i 

s  —  | 

—\ 

FIG.  67. 


Section  at  xy. 


FIG.  68. 


Sec f ion  at  tvz . 


the  distance  between  the  main  and  auxiliary  valve  center-lines  when  the  auxiliary  block  is  in  its 
cutting-off  position  as  shown  in  Fig.  68. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  57 

Then  S  =  the  distance  from  t  to  the  main  valve  center-line  minus  the  distance  from  a!  to  the  aux- 
iliary valve  center-line  =  t  u  —  a'  I'.  If  the  latest  auxiliary  cut-off  be  assumed  when  the  ciank  is  in 
the  position  C  H  (Fig.  66),  the  blocks  R  and  P  (Fig.  68)  may  be  designed  so  that  they  are  zero  dis- 
tance apart  (the  points  b'  and  c'  will  then  be  at  I'),  at  which  time  S  is  a  maximum  and  equals  C  H  in 
Fig.  66.  All  earlier  cut-offs  may  be  obtained  by  separating  the  blocks  and  thus  reducing  the  value  of  S. 

For  cut-off  at  C  P  (perpendicular  to  C  G,  Fig.  66),  S  would  be  zero  because  C  P  has  no  intercept  in 
the  relative  valve  circle,  both  valves  being  the  same  distance  off  center  and  consequently  having  zero 
distance  between  their  «enter-lines.  For  cut-off  earlier  than  this,  the  value  of  >S  would  be  negative, 
being  measured  on  the  extension  of  the  crank  line,  as  C  T7  and  C  I  at  crank  cut-off  positions  C  0  and 
C  N,  respectively;  and  these  values  would  appear  as  auxiliary  laps,  or  the  amount  that  k'  would 
overlap  t,  Fig.  68,  when  the  two  valves  are  relatively  centered. 

The  earliest  possible  auxiliary  cut-off  would  be  at  the  main  valve  admission,  which  in  this  prob- 
lem (there  being  no  lead)  would  occur  at  C  Z,  Fig.  66.  Then  S  would  equal  —  C  E,  and  the  distance 
between  the  blocks  (call  it  2  F)  would  be  a  maximum. 

If  W  =  the  width  of  the  blocks  R  and  P,  and  F  =  the  distance  the  inside  edge  of  the  block  is 
from  the  auxiliary  valve  center-line  ( =  b' I'  for  position  shown  in  Fig.  68),  we  have  for  the  general  case, 

L  =S  +  W  +  Y    .  .(1) 

While  L  and  W  remain  constant  S  and  F  vary  for  different  cut-offs,  as  the  following  cases,  Fig.  66, 
will  show,  but  the  algebraic  sum  of  Y  and  S  is  a  constant : 
For  cut-off  at  C  H,  Fig.  66,  S  =  C  H,       and  Y  =  0. 

"CX,  S  =  CX,         "    Y  =  CH-CX. 

"  CP,  S  =  0,  "     Y  =  C  H. 

"CZ,  S  =  -  C  E,    "     Y  =  CH  +  CE. 

Therefore  the  latter  value  of  F  is  the  greatest  it  can  have  between  the  above  limits  of  cut-off. 
By  substituting  any  of  the  corresponding  values  of  F  and  of  S  above  in  equation  (1),  the  value  of  L 
can  be  obtained.  Taking  the  corresponding  values  of  Y  and  S  for  cut-off  positions  C  Z: 

L=  -  C  E  +  W  +  CH  +  CE 

=  W  +  CH         .       .  •  (2) 

Width  W  of  Cut-Off  Blocks. 

The  relative  valve  motion  should  never  be  so  great  that  the  inside  edge  of  the  block  uncovers  the 
inlet  passage,  t  n  b  c,  Fig.  68.  To  obtain  a  width  to  insure  this  at  all  times,  it  is  necessary  to  consider: 

1.  The  very  earliest  cut-off  when  the  crank  is  in  the  position  C  Z.     Y  then  has  its  maximum 
value,  and  the  edge  a'  k',  Fig.  68,  is  directly  over  the  edge  t  b,  and  the  center  of  the  auxiliary  valve  the 
distance  C  E  (Fig.  66)  to  the  right  of  the  main  valve  center,  or  in  position  shown  by  dotted  line  I". 
The  outside  edge  a'  k'  would  then  have  to  move  the  distance  C  E  beyond  t  before  the  two  valves 
are  again  centered  with  respect  to  each  other. 

2.  After  the  valves  are  centered,  allowance  must  be  made  for  the  maximum  distance  the  valves 
move  apart,  C  G,  which  distance  the  edge  a'  k'  may  move  still  farther  beyond  t. 

3.  The  edge  a'  k'  has  now  moved  the  distance  C  E  +  C  G  beyond  t,  and  the  width  of  the  block 
must  be  sufficient  to  equal  this  and  also  cover  the  passageway  t  n. 

4.  In  addition,  the  block  in  its  extreme  position  should  still  have  a  small  amount  overlapping  the 
edge  n.     One-quarter  of  an  inch  may  be  allowed  for  this. 

To  sum  up,  W  =  C  E  +  C  G  +  t  n  +  %  inch. 
By  substituting  this  value  of  W  in  equation  (2), 

L^CE  +  CG  +  tn  +  %  inch  +  C  H (3) 

7 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


58 


Hence,  2 L,  or  the  distance  from  t to  r  (Fig.  68),  equals  2(CE  +  CG  +  CH  +  % inch)  +  2  width 
of  steam-inlet  passageway.  The  width  t  n  of  the  steam-inlet  passageway  may  be  made  Y*  inch 
greater  than  the  width  b  c  of  the  steam-port  opening. 

In  drawing  the  valve  for  this  problem  place  the  blocks  so  that  cut-off  occurs  at ...  .stroke.  The 
valve  drawing  in  Fig.  68  is  laid  out  to  correspond  approximately  with  the  Zeuner  diagram,  Fig.  66,  for 
cut-off  when  the  crank  is  in  the  position  C  V, . 


FIG.  G9. 

The  dimensions  shown  on  the  valve  in  the  accompanying  drawing  are  to  be  used  in  laying  out  the 
drawing  for  this  problem.  Students  may  omit  the  top  view. 

In  designs  for  this  valve  the  value  for  the  distance  6  k  may  come  out  so  large  that  the  width  of  the 
exhaust-port  is  excessive;  sometimes  there  is  room  to  divide  the  exhaust-port  and  the  valves  in  two 
parts,  as  shown  in  the  drawing.  Should  there  not  be  room  in  the  present  problem  to  permit  of  this 
division,  omit  the  part  U  and  run  the  two  exhaust  cavities  under  the  main  valve  into  one.  Or,  as 
the  problem  permits,  the  passageways  t  n  b  c  and  r  q  j  k  may  curve  either  towards  or  away  from 
the  center. 

In  the  finished  drawing  place  sufficient  dimensions  for  a  working  design.  Place  the  points  A  and 
K  of  the  valve-seat  so  that  the  edges  a  and  I  of  the  valve  will  overtravel  %  inch. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


59 


In  valves  of  the  2d  class,  which  are  operated  by  four  independent  parts,  the  most  important  type 
is  the  Corliss  valve,  shown  in  Fig.  69. 

CORLISS  VALVE-GEAR. 

The  original  type  of  valve-gear,  known  as  the  "Corliss,"  was  patented  by  Mr.  G.  H.  Corliss  of 
Providence,  R.  I.,  in  1849.  This  type  of  gear  was  subsequently  taken  up  by  numerous  manufac- 
turers, who  substituted  various  alterations  in  details  of  the  design,  until  now  such  names  as  Harris- 
Corliss,  Allis-Corliss,  etc.,  are  common. 

Fig.  69  shows  a  Corliss  engine,  one-half  in  section  and  one-half  in  full  front  view.     The  names  of 


FIG.  70. 

the  parts  operating  on  the  valve-stem  at  E  are  shown  in  Fig.  70,  on  an  enlarged  scale.     The  other 

parts  are 

A,  steam-pipe  opening.  B  And  E,  steam-valves.  C  and  K,  exhaust-valves. 

D,  exhaust-pipe  opening.  F,  radius-rods.  I,  dashpot. 

G,  dashpot-rod.  H,  wrist-plate. 

The  detail  of  the  dashpot  will  be  shown  in  a  later  sketch. 

The  Corliss  valve  may  be  considered  as  a  plain  D-valve  with  its  outside  and  inside  laps  sep- 
arated into  four  independent  parts,  and  one  placed  at  each  corner  of  the  engine  cylinder. 

Advantages:  Short,  direct  passages  reducing  steam  clearance;  reduced  valve  motion,  each 
valve  being  designed  to  move  only  a  little  after  port  is  closed  and  then  remain  at  rest  until  time 
to  open  again. 


60 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


Detail  and  Operation  of  Releasing  Gear. 

Fig.  70  is  for  valve  about  to  open,  Fig.  71  for  valve  about  to  close.  A  is  a  bell-crank  lever 
mounted  loosely  on  the  valve-stem.  V  is  the  valve-stem.  One  arm  of  A  carries  a  pin  for  rod  to 
wrist-plate;  the  other  a  pin  on  which  swings  freely  the  grab-hook  H.  Hook  H  is  pressed  in  by 
spring  S  so  that  one  arm  is  always  held  firmly  to  knock-off  cam  C,  which  is  also  loose  on  the  valve- 
stem.  Cam  C  has  an  arm  to  which  is  attached  the  governor-rod  (see  g,  Fig.  69)  to  the  governor. 
Drop  lever  B  is  keyed  to  the  valve-stem  and  connected  to  the  dashpot  by  a  rod;  it  also  carries 
a  steel  block,  or  die,  which  engages  with  the  die  on  the  grab-hook  arm. 

A  movement  of  the  cam  C  to  the  left  by  the  governor-rod  will  cause  the  hook  to  strike  the  cam- 
projection  earlier  and  the  steel  blocks  to  disengage  sooner,  thus  giving  earlier  cut-off;  when  the  gov- 
ernor-rod pulls  to  the  right  the  cut-off  will  occur  later. 

Different  makers  substitute  different  forms  for  cam  C.  A  common  -form  is  to  have  a  plain 
hub  with  steel  knock-off  block  bolted  on,  etc.  The  principle,  however,  is  the  same  in  all. 

Fig.  72  shows  center-line  sketch  of  Corliss  valve-gear;  full  lines  for  eccentric  in  extreme  left- 
hand  position;  dotted  lines  (No.  2)  for  opening  and  closing  position  of  the  valve,  and  lines  (No.  3) 


GOVERNOR 


TOWftJST-PLATE 


H 


FIG.  71. 

for  extreme  clockwise  eccentric  position.  Diagram  shows  small  amount  of  travel  of  valve  when 
port  is  closed  as  compared  to  that  when  open  by  the  angles  marked  " closed"  and  "open."  This 
is  an  essential  feature  of  the  valve;  giving  as  it  does  quick  travel  at  steam-port  opening,  and  reduc- 
ing its  entire  travel  to  a  minimum.  The  adjustment  of  the  angles  for  the  valve  arms  and  rods 
is  a  matter  of  trial-and-error  until  desired  results  are  produced;  they  may  be  placed  above  the 
valve  (as  shown  in  Fig.  72),  or  below,  (Fig.  69)  according  to  the  circumstances  surrounding  the 
design. 

Angles  a  are  the  same,  radial  line/  passing  through  edge  of  port,  and  similar  line  g  through  edge 
of  valve  for  extreme  closed  position.  Sectional  and  dotted  outlines  show  extreme  positions  of 
valve.  Exhaust  valve  has  a  positive  motion,  i.e.,  has  no  automatic  releasing  gear  as  has  the  steam 
valve. 

Corliss  valves  may  be  single-ported  (Fig.  72),  or  double-ported  (Fig.  73). 


VALVES,   VALVE-GEARS   AND   VALVE   DIAGRAMS 


61 


Limited  Range  of  Cut-Off  With  Single  Eccentric. 

The  Corliss  valve-gear  with  single  eccentric  will  operate  the  cut-off  automatically  only  up  to 
half  stroke  as  the  following  argument  will  show: 

When  release  occurs,  the  main  crank  has  not  quite  reached  the  dead-point;  also,  when  compres- 
sion occurs,  the  crank  has  not  reached  the  other  dead-point.  When  the  crank  is  half-way  between 
the  positions  corresponding  to  release  and  compression,  it  is  still  shprt  of  the  90°  position,  and  the 


FIG.  72. 

piston  is  short  of  half-stroke.  When  the  crank  is  in  this  "  half-way  "  position,  the  exhaust-valve, 
the  exhaust-valve  radius-rod  and  the  wrist-plate  are  all  at  extreme  throw,  for  the  exhaust-valve  is  in 
exactly  the  same  positions  at  release  and  compression,  and  its  motion  comes  indirectly  from  the  main 
crank  shaft.  When  the  wrist-plate  is  at  extreme  throw  the  grab-hook  is  in  its  highest  position 
and  if  it  does  not  strike  the  governor  cam  by  the  time  it  reaches  this  highest  position  it  will  not  strike 
it  at  all.*  But  it  has  been  seen  that  the  wrist-plate  (and  therefore  the  grab-hook)  reaches  its  extreme 

*  In  this  event  the  blocks  on  the  grab-hook  and  valve-stem  arms  will  remain  in  engagement  during  the  entire 
«ycle  and  cut-off  will  occur  at  or  near  the  end  of  the  stroke. 


62 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


throw  before  half-stroke.  Therefore,  automatic  cut-off  by  the  dashpot  cannot  occur  later  than 
half-stroke.  When  this  is  understood  it  will  be  seen  that  the  exhaust  steam  requirements  at  one  end 
of  the  cylinder  actually  control  the  latest  point  of  cut-off  on  the  other  end  of  the  cylinder  when  a 
single  eccentric  is  used. 

In  good  indicator  cards  from  fast  running,  single  eccentric,  Corliss  engines,  it  sometimes  appears 
that  cut-off  takes  place  later  than  half  stroke.  This  is  only  apparent,  however,  as  the  cut-off 
actually  begins  before  half  strode,  but  the  relatively  fast  moving  piston,  which  is  at  its  maximum 
at  about  the  middle  of  the  stroke,  gets  past  the  center  before  the  valve  (even  when  operated  by  a 
good  dashpot)  closes  the  steam-port.  The  following  calculation  may  show  this  more  clearly: 

A  good  vacuum  dashpot  closes  the  valve  in  about  TV  second,  or  during  TV  of  a  revolution  for 
engine  running  96  revolutions  per  minute.  This  is  approximately  \  of  the  stroke  at  the  center, 
which  must  be  added  to  the  per  cent,  of  stroke  when  steam  hook  strikes  knock-off  block  or  cam, 


FIG.  73. 

to  give  actual  final  point  of  cut-off.  100  to  120  revolutions  per  minute  may  be  assumed  as  prac- 
tical limit  of  speed  of  engine  with  this  type  of  gear,  owing  to  wear  of  releasing  mechanism,  and 
comparatively  slow  action  of  dashpot. 

A  greater  range  of  cut-off  may  be  obtained  by  using  two  eccentrics  and  two  wrist-plates,  one 
set  for  the -steam  valves  and  the  other  for  the  exhaust  valves. 

The  length  of  the  steam  and  exhaust  ports  is  made  nearly  equal  to  the  diameter  of  the  cylinder 
bore,  as  a  rule.  Steam  and  exhaust  valves  are  usually  made  of  equal  diameter,  and  vary  from 
%  cylinder  bore  in  small  engines  to  H  in  larger  ones.  For  steam-port,  a  steam  velocity  of  8000 
feet  per  minute  may  be  allowed;  for  exhaust-port,  6000. 

Setting  Corliss  Valve-Gear. 

"  Adjust  length  of  eccentric-rods  to  give  wrist-plate  equal  travel  on  both  sides  of  center  mark 
on  bracket.  Adjust  radius-rods  to  give  proper  lap  with  wrist-plate  in  central  position.  Move 
wrist-plate  to  end  of  its  travel  either  way,  and  adjust  length  of  dashpot-rods  to  let  hooks  engage 
freely  on  catch-blocks.  Put  crank  on  dead-center,  and  set  eccentric  ahead  of  crank  enough  to 
give  desired  lead.  Raise  governor  to  highest  working  position,  and  adjust  length  of  governor- 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


63 


rods  so  that  the  knock-off  cams  will  just  keep  hooks  off  catch-blocks — or  some  initial  motion  may 
be  allowed,  but  not  enough  to  open  the  port. " 

Dashpots  are  of  various  forms  and  construction,  the  principle  in  all  cases  being  that  a  vacuum 
is  used  to  accelerate  the  fall  of  the  plunger,  or  bell  (A,  Fig.  74).  An  air  cushion  is  provided  to 
bring  the  plunger  to  rest  without  shock.  Fig.  74  represents  a  well-known  design.  In  this  case 
C  is  the  dashpot-rod  leading  to  the  drop  lever  which,  in  turn,  is  keyed  to  the  valve-stem.  The 


FIG.  74. 


ball  joint  is  used  to  accommodate  a  slight  swing  of  the  rod.  The  vacuum  is  created  between  A  and 
B.  B  may  be  termed  a  "stationary  piston."  D  is  a  regulation  screw  with  locknut  E.  Through 
D  is  drilled  a  small  hole  with  side  outlets  just  above  the  cone  seat,  as  shown.  Any  air  pressure 
which  might  accumulate  in  the  vacuum  space  is  expelled  through  small  drilled  holes  leading  to 
the  under  side  of  the  ball  seat  at  F.  The  air  cushion  is  formed  and  acts  while  the  point  x  of  the 
flange  A,  of  the  plunger  is  passing  from  y  to  z.  The  cushioning  effect  is  adjusted  by  the  solid 


64 


VALVES,   VALVE-GEARS  AND   VALVE  DIAGRAMS 


thumb  screw  H,  which  regulates  the  flow  of  air  from  the  passage  M  through  the  opening  K  to  the 
space  N.  G  is  the  body,  and  R  the  cover  of  the  dashpot.  The  circular  grooves  0  P  Q,  etc.,  are 
for  lubrication.  The  sloping  edges  tuvwy  are  designed  to  prevent  a  too  sudden  cushioning  effect. 


DRAFTING  TABLE  PROBLEM,  No.  5 — CORLISS 
Data  for  Problem: 

Bore  of  cylinder.  .12".     Distance  between  centers  of  valves   (horizontal)  32". 

"  "  "      "      "        (vertical)       16". 

Radius  to  hook-rod  pin  on  swing-plate 8". 

"        radius-rod  pin  on        "          6". 


VALVE-GEAR. 


Stroke 24". 

Bore  of  all  valves .  3". 
Eccentric  throw. . .  3". 
Diam.  of  hub  circle  5". 


Method  of  procedure :  (Reference  letters  belong  to  Fig.  75) . 

1.  Locate  centers  of  valves  a,  b,  c,  and  d. 

2.  Draw  in  circles  representing  bore  of  valves. 

3.  Locate  center  of  s wing-plate (e). 

Bent  Rocker  to  Neutralize  Angularity  of  Connecting-Rod. 

4.  Draw  rocker  /  e  g  with  upper  arm  vertical,  and  lower  one  at  15°  with  vertical  center-line. 
This  angularity  is  introduced  to  help  correct  angularity  of  the  connecting-rod.     This  position  of  the 

(Central  Position. 
Note  <  Full -Throw  Forward. 
(flill-Thron  Return.- 


FIG.  75. 


rocker  is  its  central  position  corresponding  to  zero  throw  of  the  eccentric.  The  rocker/  e  g  in  prac- 
tice (in  long-frame  engines)  is  placed  at  some  convenient  point  between  the  cylinder  and  the  shaft, 
the  eccentric-rod  connecting  to  the  point  g,  and  one  end  of  the  hook-rod  to  /.  The  other  end  of  the 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


65 


hook-rod  is  attached  to  a  point  on  the  swing-plate  occupying  the  same  position  as  /.  The  points, 
h,  i,  y,  etc.,  are  also  on  the  swing-plate.  The  rocker,  in  designing,  is  shown  attached  to  the  swing- 
plate  shaft  for  convenience  and  to  save  space  in  the  lay-out. 

5.  Show  rocker-pins  /  and  g  with  a  diameter  of  1  inch,  and  draw  indefinite  arcs  on  which  the 
extreme  travels  of  /  and  g  will  be  shown  later. 

6.  Lay  off  eccentric-throw  from  g,  and  locate  extreme  positions  of  rocker-pins  for  full  throw 
forward  stroke  (g1  and/,)  and  full  throw  return  stroke  (gy  and/J. 

7.  Draw  all  arms,  links,  etc.,  in  solid  lines,  and  cross-section  all  circles,  for  the  zero  eccentric- 


FIG.  76. — Section  of  Atlas  Cylinder. 


FIG.  76a. — View  of  Atlas  Engine. 

throw  position.     For  arms,  links,  etc.,  in  full  throw  forward  and  return  stroke  positions  use  character- 
istic lines  shown  in  sketch,  and  leave  circles  open. 

8.     Locate  radius-rod  pins  h  and  i  on  swing-plate  3  inches  apart.      This  is  the  minimum  dis- 
tance-to allow  for  machining  and  play  between  the  rod  ends.     Make  pins  h  and  i  %  inch  in 
diameter.     Show  these  pins  in  extreme  forward  and  return  positions. 
9.     Make  steam-port  width,  j  k  =  H  inch. 

10.  Make  steam-lap,  kl  =  -fa  inch. 

11.  Make  width  of  passage  through  valve,  I  m  =  IH  inches. 

Determination  of  Valve  Travel  for  Cylindrical  Valve. 

12.  Find,  by  method  of  trial-and-error,  the  point  n  of  the  rod  n  h  and  rocker-arm  n  a  so  propor- 
tioned as  to  turn  point  I  of  valve  to  lt  (I  travels  a  small  distance,  say  %,  inch,  beyond  j  so  as  to 


66 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


produce  more  uniform  wear  on  valve  and  valve-seat)  while  h  travels  to  h,.  Mark  the  corresponding 
extreme  point  of  travel  of  n  at  n, ;  also  mark  the  other  extreme  point  of  travel  for  n  at  n2  when  h 
reaches  /i2.  The  lines  a  nl  and  n,  h1}  and  also  ft2  h^  and  ft,  e  must  not  be  allowed  to  reach  a  straight 
line  position.  This  trial-and-error  process  is  usually  accomplished  by  a  stiff  paper  model  on  a  full 
scale;  but  as  a  student  exercise  it.  may  be  done  with  two  pairs  of  dividers,  or  with  dividers  and  com- 
pass. The  length  of  the  arm,  a  n,  may  be  assumed  as  4  inches. 

13.  Locate  points  on  crank  end  of  steam-valve  corresponding  to  the  points  n,  nl  and  w.r     The 
same  arguments  and  methods  apply,  but  the  results  are  slightly  different. 

Determination  of  Travel  of  Piston  of  Dashpot. 

14.  Assume  that  the  drop-lever  pin  travels  in  an  arc  with  a  radius,  a  q  =  a  n,  thus  determining 
the  rise  of  the  dashpot  plunger.     For  less  rise  a  shorter  radius  would  be  used. 

15.  Drop-lever  pin  q  should  move  equal  distances  on  each  side  of  horizontal  center-line.     The 


M 


FIG.  77.— Section  through  D  E  of  FIG.  77a. 

pins  n  and  p  on  the  rocker-arms,  and  the  latch-pin  q  must  all  swing  through  the  same  length  of  arc 
=  ny  n,.     Therefore  lay  off  points  #,  and  &  symmetrically  about  the  center-line  a  d. 

16.  <?2  and  ql  correspond  to  extreme  hook-latch  positions.     The  distance  between  the  hook 
latch  and  the  pin  on  the  rocker  must  be  great  enough  to  allow  hub  and  arm  length  of  hook  to  main- 
tain latch  effect,  if  desired,  to  end  of  swing.     This  distance  is  determined  practically  by  the  design  of 
the  hook,  and  in  this  problem  the  distance  between  ga  and  p^  may  be  assumed  to  be  great  enough  if  an 
angle  of  30°  (g,  a  p2)  is  taken. 

17.  With  the  point  p2  determined,  the  angle  between  the  two  arms  (p2  a  and  a  wj  of  the  rocker  is 
determined.     Lay  off  the  central  and  extreme  forward  positions  of  the  arm  p.,  a. 

18.  Determine  corresponding  points  for  steam-valve  on  the  crank  end. 

19.  Lay  off  exhaust  port,  tu  =  \Y%    inches;    exhaust-lap,  u  v  =  ^  inch,  and  exhaust  port 
through  valve,  \1A  inches. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


67 


Avoidance  of  Dead-Points  in  Valve-Gear  Mechanism. 

20.  By  trial-and-error  adjust  the  length  of  the  valve-arm  6  x  (it  is  to  be  noted  that  the  exhaust 
valve  is  never  closed  by  a  dashpot,  and  that  it  remains  under  the  control  of  the  wrist-plate  all  the 
time),  and  the  link  x  y,  so  that  v  just  over  travels  t  to  z,  which  gives  smooth  wearing  effect.  Neither 
b  x  and  x  y,  nor  x  y  and  y  e  should  cross  a  "dead-center"  between  their  extreme  positions.  Locate 
central  and  extreme  positions  of  the  arms  and  links  operating  this  valve. 


FIG.  77a. — Section  through  M  N  of  FIG.  77. 

21.  Make  the  exhaust  valve-arm  at  c  the  same  length  as  that  determined  at  b,  and  draw  in  the 
central  and  extreme  positions. 

22.  In  addition  to  showing  the  arms  and  links  throughout  for  the  three  positions  in  character- 
istic line  work,  the  passage-ways  in  the  valves  themselves  must  be  indicated  by  the  same  character 
of  line  work,  as  per  example  at  6.     Place  24-inch  circles  at  all  pin  joints,  except  on  the  large  rocker 
feg. 

23.  Place  dimensions  at  all  points  indicated  in  the  sketch.     Place  the  words  "Forward"  and 
"Return"  in  their  proper  places  on  the  two  arrows. 


68  VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 

EXAMPLES   OF   PRACTICAL  VALVE  CONSTRUCTION. 

The  Corliss  form  of  valve  is  used  in  a  number  of  different  makes  of  steam  engines  that  are  not 
classed  as  Corliss  engines,  an  example  being  one  of  the  types  manufactured  by  the  Atlas  Engine 
Works  and  illustrated  in  Figs.  76  and  76a.  The  live  steam  valves  are  shown  at  a  and  b,  are  double 


FIG.  78.— Wheelock  Valves. 


ported,  and  are  both  operated  by  the  same  eccentric  and  shaft-governor.  The  exhaust  valves  at 
c  and  d  are  also  double  ported  and  are  operated  by  a  single  fixed  eccentric.  A  characteristic  feature 
of  this  engine  is  the  location  of  the  cylindrical  valves  in  the  cylinder  heads,  thus  giving  the  shortest 
possible  steam  and  exhaust  ports,  and  small  clearance  space. 


FIG.  79. — Buckeye  Flat  Valves. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


69 


A  prominent  valve  of  the  Polonceau  type,  and  combining  the  features  of  the  double  valve,  and 
the  four-part  valve,  is  shown  in  Figs.  77  and  77a.  It  is  also  one  of  the  pronounced  types  of  the  grid- 
iron valve,  and  is  used  on  the  Mclntosh,  Seymour  &  Go's,  engine.  The  section  shown  (Fig.  77)  lies 
in  a  transverse  plane  (D  E  of  Fig.  77a)  close  to  the  cylinder  head.  A  is  the  valve-seat,  B  the  main 
valve,  and  C  the  auxiliary  or  cut-off  valve.  There  are  two  such  valves,  one  at  each  end  of  the 
cylinder  for  the  admission  of  live  steam.  In  the  two  exhaust  valves  the  auxiliary  block  is  omitted. 
The  advantage  of  the  gridiron  valve  is  small  travel  and  friction,  while  it  may  be  set  to  give  small 
clearance  and  be  operated  by  gearing,  as  shown  in  Fig.  77,  to  give  practically  no  motion  when  idle, 


FIG.  80. — Buckeye  Round  Valve. 

and  to  give  cut-off  at  or  near  its  maximum  velocity.  Its  disadvantages  are,  delicate  adjustment  for 
lead  owing  to  the  numerous  divisions  of  the  port,  limited  range  of  cut-off,  and  expensive  construc- 
tion. 

A  valve  of  the  Gonzenbach  type  is  the  one  belonging  to  the  Wheelock  engine,  shown  in  longitud- 
inal section  in  Fig.  78.  Although  it  has  four  independent  parts,  it  belongs  properly  to  the  double- 
valve  class,  with  one  set  of  parts  at  each  end  of  the  cylinder.  A  is  the  main  valve,  which  is  designed 
to  govern  admission,  release,  and  compression  and  B  the  auxiliary,  which  is  designed  to  regulate  cut- 
off only,  and  which  is  operated  by  a  tripping  mechanism  under  control  of  the  governor. 

A  special  valve  of  the  Polonceau  type  is  that  used  on  the  Buckeye  engine,  as  shown  in  Fig.  79. 
The  parts  marked  A  form  a  steam-tight  box,  except  at  the  opening  E  and  the  port  F,  and  comprise 
the  main  valve.  The  blocks  C  form  the  auxiliary,  or  cut-off  valve,  which  is  operated  through  the 
rod  D  and  a  rotating  eccentric,  by  the  fly-wheel  governor.  B  is  a  hollow  valve-stem  operating  the 
main  valve  through  a  separate  eccentric  keyed  permanently  to  the  shaft.  The  two  valve-stems  B 
and  D  receive  their  motion  through  a  compound  rocker  peculiar  to  this  type  of  valve-gear.  The 
main  and  cut-off  valves  each  have  uniform  travel,  and  both  are  arranged  so  that  cut-off  takes  place, 
whether  early  or  late,  when  the  cut-off  valve  is  moving  at  or  near  its  fastest  rate. 

Piston-valves  mav  also  be  used  to  give  an  independent  cut-off,  as  shown 'in  Fig.  80.    / 


70  VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 

SECTION  IV.— ECCENTRICS  AND  SHAFT-GOVERNORS. 

ECCENTRICS. 

An  engine  is  "reversed"  when  its  direction  of  running  is  changed  from  "over"  to  "under" 
or  vice  versa,  and  is  usually  accomplished  by  a  special  form  of  gear  or  link-mechanism  between 
the  valve  and  main  shaft. 

When  the  valve  and  eccentric  are  direct  connected  "reversal"  can  only  be  obtained  by  a  wide 
movement  of  the  eccentric.  Eccentrics  that  move  automatically  by  means  of  the  centrifugal 
force  due  to  weights  in  the  fly-wheel,  generally  have  a  narrow  motion  and  permit  the  engine  to 
run  in  one  direction  only  but  with  variable  cut-off.  In  the  eccentrics  treated  below,  they  will, 
for  completeness  of  analysis,  be  assumed  to  have  a  wide  range  of  motion  from  full  speed  forward 
or  "over,"  to  full  speed  backward  or  "under." 

Classification  of  Eccentrics. 

All  eccentrics  may  be  divided  into  three  classes: 

(1)  Fixed  eccentrics,  in  which  the  valve-travel  always  remains  the  same;  likewise  the  angle 
of  advance  unless  the  engine  is  stopped  and  the  eccentric  rekeyed  or  refastened  in  another  position. 
See  Fig.  81. 

(2)  Rotating  eccentrics,  in  which  the  valve-travel  always  remains  the  same  but  the  angle  of 
advance  changes  automatically  according  to  the  load.     See  Figs.  82  and  89. 

(3)  Slotted  eccentrics,  in  which  the  valve-travel  and  the  angle  of  advance  both  change  at 
the  same  time  automatically,  according  to  the  load.     Slotted  eccentrics  are  subdivided  into, 

(a)  Swinging  .or  curved-slot  eccentrics.     See  Figs.  83,  87  and  88. 

(b)  Straight-slot  eccentrics.     See  Figs.  84  and  93. 

Reversing  With  Eccentrics. 

To  reverse  an  engine  with  any  one  of  these  eccentrics,  it  would  be  necessary  to  move  the  eccen- 
tric-center from  c  or  d  (Figs.  81-84)  to  /or  g,  as  may  be  seen  in  Figs.  85  and  86,  where  the  eccen- 
tric has  been  moved  from  a  c  to  a  g.  The  arrows  on  the  crank  show  the  resultant  change  in  the 
direction  of  running.  In  every  case,  Figs.  81  to  84,  I  a  c  is  the  angle  of  advance  and  a  c  the  half 
valve-travel  for  one  position  of  the  eccentric,  I  a  d  is  the  angle  of  advance  and  a  d  the  half-travel 
for  another  position  of  the  eccentric,  etc. 

Exercises  Showing  the  Relations  Between  Eccentric  Positions  and  Zeuner  Diagrams. 

As  essential  exercises  the  student  should  here  draw  diagrams  similar  to  Figs.  85  or  86,  assum- 
ing sizes  for  all  parts  and  angle  of  advance . 

(1)  For  engine  running  over,  with  crank  set  at  dead-center,  crank  end. 

(2)  For  engine  running  over  with  straight  reversing  rocker-arm  (see  Fig.  25)  when  the  crank 
is  on  dead-center,  head  end. 

Other  exercises  necessary  to  a  full  understanding  are : 

(3)  The  drawing  of  Zeuner  diagrams  for  head  end  only  for  the  eccentric-center  positions, 
c,  d,  e  and  g  in  Figs.  82-84.     Draw  these  diagrams  double  size  and  assume  the  same  steam-  and 
exhaust-laps  throughout,  and  note  the  effect  on  lead,  and  on  the  four  principal  crank  positions. 

Referring  to  Figs.  87-89,  a  is  the  shaft  center,  b  the  eccentric-center,  a  b  the  half  valve- 
travel,  e  a  b  the  angle  of  advance,  and  a  r  the  crank  position  in  each  case. 


FIG.  83. — Swinging  or  Curved-Slot  Eccentric 
7 


FIG.  81. — Fixed  Eccentric. 


FIG.  84. — Straight-Slot  Eccentric 


FIG.  82.— Rotating  Eccentric 


FIG.  85. — Running  "Over." 


m 


FIG.  86.— Running  "Under." 


FIG.  87. — Westinghouse  Shaft-Governor. 


FIG.  88. — "Straight-Line"  Engine  Governor. 


FIG.  89. — Buckeye  Shaft-Governor. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  73 

EXAMPLES  OF  PRACTICAL  ECCENTRIC  AND  GOVERNOR  CONSTRUCTION. 

The  Westinghouse  shaft-governor,  Fig.  87,  has  a  curved-slot  eccentric.  It  is  shown  with  the 
governor  weights  c  and  d  full  out.  The  eccentric  swings  about  the  point  o  on  the  fly-wheel  arm. 
The  governor  weights  swing  about  the  points  /  and  g  respectively,  also  on  the  fly-wheel. 

The  Straight-Line  engine  governor,  Fig.  88,  has  also  a  curved-slot  eccentric.  It  is  shown  with 
the  governor  weight  in,  and  as  the  engine  speeds  up  the  eccentricity  is  reduced  and  the  angle  of 
advance  increased.  This  eccentric  is  swung  about  a  pivot,  o,  specially  located  so  as  to  give  a  posi- 
tive lead  for  %  to  %  cut-off  and  a  negative  lead  at  the  shorter  cut-offs.  The  purpose  of  this  is 
to  neutralize  to  some  extent  the  results  of  too  early  compression  and  release  on  short  cut-offs 
and  too  little  compression  on  late  cut-off,  all  of  which  follow  from  shifting  eccentrics. 

The  Buckeye  governor,  Fig.  89,  shows  a  rotating  eccentric  with  minimum  angle  of  advance  and 
latest  cut-off. 

Effect  of  Location  of  Pivot  in  Curved-Slot  Eccentrics. 

In  using  the  curved-slot  or  swinging-eccentric,  it  makes  a  difference  which  side  of  the  shaft 
the  eccentric  is  pivoted  on,  as  Fig.  90  will  show.  The  solid  part  of  this  figure  is  similar  to  i'ig. 
83.  The  dotted  lines  are  added  to  represent  the  eccentric  if  it  were  designed  to  swing  about  r  instead 


FIG.  90. 


of  a.  6  is  the  center  of  the  main  shaft,  c  is  the  center  of  the  eccentric-sheave  and,  for  the  posi- 
tion shown,  s  b  c  is  the  angle  of  advance,  and  6  c  the  eccentricity. 

If  the  eccentric  is  moved  about  a  so  as  to  give  the  angular  advance  sb  d,  c  will  go  to  d  and  6  d 
will  be  the  eccentricity. 

If  the  eccentric  is  moved  about  r  so  as  to  give  the  same  angular  advance  s  b  d,  c  will  go  to  o 
and  6  o  will  be  the  eccentricity. 


74 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


When  c  reaches  e  the  engine  is  in  mid-gear,  and  if  c  were  moved  to  c'  the  engine  would  be  in  full- 
gear,  running  in  reverse  direction.  By  constructing  a  series  of  Zeuner  circles  with  the  angles  of 
advance  sb  c,  sb  d,  and  sb  e  (see  Figs.  91  and  92),  it  may  be  shown  that  the  lead  increases  largely 
toward  mid-gear  by  using  pivot  a,  and  that  it  is  reduced  toward  mid-gear  by  using  pivot  r.  It 
should  be  noticed  that  while  the  lead  increases  in  one  case  and  decreases  in  the  other,  the  angle 
of  lead  increases  in  both,  but  at  a  much  slower  rate  in  Fig.  92. 

The  forms  of  shaft-governors  already  illustrated  show: 

1.  The  eccentric  which  turns  on  the  shaft,  giving  always  the  same  valve-travel  but  varying 
angles  of  advance,  Fig.  89. 

2.  The  swinging-  or  curved-slot  eccentric,  Figs.  87  and  88. 
The  following  illustrations  show: 

3.  The  straight-slot  eccentric,  Figs.  93  and  94,  and  the  equivalent  of  the  straight-slot  eccen- 
tric, Figs.  95-97,  which  illustrate  the  Armington  and  Sims  governor. 


\C 


\ 


4.  The  swinging  pivot,  which  takes  the  place  of  the  swinging  eccentric,  Fig.  98,  illustrating 
the  American-Ball  engine.  The  complete  engine  is  shown  in  perspective  outline  in  this  case,  so 
that  the  student  may  form  a  comprehensive  idea  of  a  complete  set  of  connections  from  the  gov- 
ernor mechanism  to  the  valve.  In  all  the  other  governor  illustrations  here  given  the  eccentric- 
rod  k  screws  into,  or  is  bolted  to,  the  eccentric-strap  which  works  on  the  eccentric-sheave. 


VALVES,   VALVE-GEARS   AND   VALVE  DIAGRAMS 


75 


Explanations  of  Figs.  93  to  98  are  as  -follows: 

In  Fig.  93  the  frame  c  c  is  securely  attached  to  the  shaft  whose  center  is  o.  The  position  shown 
is  for  the  engine  at  rest;  as  it  speeds  up  the  weights  w  w  fly  out,  and  the  center  of  the  eccentric- 
sheave  a  moves  straight  across  and  changes  the  angle  of  advance,  for  example,  from  d  o  a  to  d  o  a', 
and  the  eccentricity  from  o  a  to  o  a',  preserving  constant  lead. 

Another  form  of  straight-slot  eccentric  is  that  manufactured  by  the  Fitchburg  Steam  Engine 
Co.,  illustrated  in  Fig.  94.  The  two  pins,  s  and  e,  in  the  eccentric-strap  move  in  short  arcs  follow- 
ing closely  the  vertical  center-line,  thus  giving  to  the  center,  6,  of  the  sheave  approximately  the  same 
straight-line  motion  as  is  secured  by  the  Watt's  parallel  motion  mechanism.  Thus  practically 
constant  lead  is  obtained.  The  weights  o  o  balance  the  weights  of  the  eccentric  and  its  strap,  and 
also  the  valve  and  valve-rods  in  vertical  engines,  taking  the  effort  to  move  these  parts  off  the  gov- 
ernor. Both  the  centrifugal  weights  act  in  unison  through  the  links,  k  c,  k  f,  and  lever  arms,  sd,ed, 
to  move  the  eccentric  as  the  engine  changes  speed.  The  engine  may  be  made  to  govern  when  run- 
ning in  a  reverse  direction  by  transferring  the  ends  of  the  connecting  links,  k  c,  kf,  from  c  to/  and 


FIG.  92. 

from/  to  c  respectively,  and  putting  on  a  new  eccentric-sheave.  The  governor,  in  the  position  drawn 
in  Fig.  94,  is  at  rest  or  running  at  very  low  speed,  r  a  being  the  position  of  the  crank,  e  ab  the  angle 
of  advance,  and  a  b  the  half  valve-travel. 

The  Armington  and  Sims  governor,  Figs.  95-97,  has  a  combination  of  two  eccentrics,  one 
being  loose  on  the  shaft  and  the  other  surrounding  it.  The  inner  eccentric  is  connected,  through 
arms  and  links,  to  weights  w  and  z  as  shown;  the  outer  eccentric  is  connected  to  w  only.  The  weights 
w  and  z  are  pivoted  to  the  arms  d  and  m  of  the  fly-wheel,  which  is  keyed  to  the  shaft  s.  Fig.  95 
shows  the  governor  mechanism  when  the  engine  is  at  rest,  and  Fig.  96  running  at  top  speed.  In  the 
latter  position  the  governor  has  a  minimum  eccentricity,  as  shown  at  s'  r'  in  Fig.  96,  and  also  in  the 


76 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


FIG.  93. 


FIG.  94. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


77 


FIG.  95. 


FIG.  96. 


center-line  sketch,  Fig.  97,  in  which  s  represents  the  center  of  the  shaft,  and  the  other  letters,  the  cor- 
responding points  of  Figs.  95  and  96. 

When  starting  up,  the  eccentricity  of  the  inner  eccentric  is  s  o  (see  Figs.  95  and  97),  that  of  the 
outer  eccentric  is  o  r  with  respect  to  the  inner  eccentric,  and  the  effective  eccentricity  of  the  combina- 
tion is  s  r,  the  angle  of  advance  being  t  s  r.  The  proportions  of  the  mechanism  are  such  that  the  the- 
oretical angle  j  or  remains  con  tant. 

As  the  speed  of  the  engine  increases,  the  points  e,  g,j,  o,  r  and  h  go  to  e',  g',f,  o',  r'  and  h'  re- 
spectively and  s  r'  becomes  the  eccentricity  and  t  s  r'  the  angle  of  advance.  If  the  path  of  r  (r  r') 


J 


FIG.  97. 


78 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


is  at  right-angles  to  the  line  of  stroke  s  d,  this  combination  of  eccentrics  will  give  the  changes  in 
both  eccentricity  and  angular  advance  with  a  constant  lead,  and  will  be  an  exact  equivalent  of  a 
straight-slot  eccentric. 

The  American-Ball  governor,  illustrated  in  Figs.  98  and  99  represents  their  latest  type  of  con- 
struction, in  which  the  governor  mechanism  is  in  gravity  balance  throughout  the  cycle.  This 
balance  is  obtained  by  so  proportioning  the  governor  arm,  b  c,  and  the  secondary  arm,  r  f,  Fig.  98, 
and  j  f,  Fig.  99,  that  the  center  of  gravity  of  the  former  is  to  the  right  of  the  center  of  rotation  a, 
and  the  center  of  gravity  of  the  latter  is  to  the  left  of  the  center  of  rotation  /.  The  two  arms  are 
connected  by  the  link  d  e.  In  proportioning  these  arms  care  is  taken  to  have  the  center  of  gravity 
of  the  secondary  arm  practically  at  the  axis  of  the  shaft  so  that  it  will  develop  no  centrifugal  force. 
Another  feature  of  construction,  recently  applied,  is  the  use  and  arrangement  of  double  springs,  as 
illustrated  at  m  n  and  m  p,  Fig.  98,  for  the  purpose  of  reducing  the  ill  effects  caused  by  swaying  of 
single  springs  due  to  centrifugal  force  and  gravitation.  It  will  be  noted  that  the  swinging  pivot  g 
takes  the  place  of  the  eccentric-sheave  and  strap  shown  in  previous  illustrations;  also,  that  the  center 
of  rotation,  /,  is  to  one  side  of  the  center-line  for  the  purpose  of  giving  larger  port  openings  at  the 
earlier  cut-offs,  a  o  g  is  the  angle  of  advance,  k  o  the  crank  position,  and  o  g  the  half-valve  travel," 
o  h  is  the  half-valve  travel  at  minimum  cut-off. 

Another  governor,  simple  in  construction  and  similar  in  action  to  that  shown  in  dotted  Fig.  90, 
and  giving  a  diagram  quite  similar  to  that  shown  in  Fig.  92,  is  manufactured  by  the  New  York  Engine 
Co.,  at  Watertown,  N.  Y.  It  is  illustrated  diagrammatically  in  Fig.  100,  k  o  being  the  crank,  nog- 
the  angle  of  advance,  g  o  the  half  valve-travel,  o  h  the  lap,  and  o  I  the  lap  plus  lead.  The  weighted 


FIG.  98. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


79 


bar,  6  6,  swings  on  the  pivot  /  which  is  secured  to  the  fly-wheel  arm;  and  its  position  is  controlled 
by  the  speed  of  the  engine  and  counteracting  spring  r  s. 


FIG.  99. 

COMPARATIVE  INDICATOR  CARDS  FROM  DIFFERENT  KINDS  OF  ECCENTRICS. 

Comparative  results  obtained  on  the  indicator  card  by  the  different  forms  of  shaft-governors  are 
illustrated  in  two  of  the  most  used  forms  in  Figs.  101  and  102.  It  will  be  seen,  in  general,  that  the 
compression,  w'}  x',  y',  increases  very  rapidly  and  becomes  very  large  with  the  earlier  cut-offs;  also 


FIG.  100. 


that  the  preadmission,  n',  o',  p',  increases  rapidly  in  Fig.  101.     The  release  also  comes  too  early  with 
the  early  cut-off  and  the  compression  too  late  with  the  late  cut-off  for  smoothest  and  most  economical 


SO  VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 

running.     Negative  exhaust  lap,  which  is  used  under  some  conditions,  has  the  effect  of  making  the 
compression  much  later  on  the  earlier  cut-offs,  and  the  release  earlier. 

Different  makes  of  shaft-governors  are  designed  to  meet  certain  average  conditions,  and  to  give 
best  action  throughout  a  certain  range  of  cut-off,  these  different  designs  leading  to  the  claims  of 
different  manufacturers.  For  example,  the  straight-slot  eccentric  gives  a  wider  range  of  cut-off, 
0.228  to  0.780  against  0.332  to  0.792  for  the  curved-slot,  Figs.  101  and  102;  the  curved-slot,  a  more 
uniform  maximum  compression,  as  may  be  seen  by  comparing  the  points,  n',  o',  p'  in  the  two  figures; 
the  straight-slot  a  smaller  range  of  preadmission;  the  curved-slot  more  area  in  the  card,  etc.,  etc., 


FIG.  101. 


FIG.  102. 


for  given  angles  of  advance.  Some  of  these  points  may  be  construed  as  advantages  or  disadvantages, 
or  as  lesser  evils,  according  as  one  sums  up  all  the  conditions  of  a  design. 

The  effects  on  the  indicator  card  are  changed  by  two  prominent  engine  manufacturers  from  those 
shown  in  Figs.  101  and  102,  one  by  placing  the  locus  of  the  eccentric  center  for  different  cut-offs  as 
shown  at  c  p  in  Fig.  92,  and  the  other,  by  placing  the  locus  approximately  in  the  position  that  /  i, 
Fig.  101,  would  have  if  the  point  /  remained  stationary  and  i  were  swung  to  the  left  in  an  arc  until  it 
met  the  horizontal  center-line  a  c. 

Since  preadmission  is,  under  ordinary  conditions,  the  most  powerful  factor  in  " compression,"  or 
smooth  running  over  the  dead-centers,  it  must  be  looked  to  critically  in  design  work.  It  will  be  seen 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


81 


from  Figs.  101  and  102  that  preadmission  is  always  variable,  even  when  the  lead  is  constant,  and  that 
the  straight-slot  eccentric  gives  the  narrower  range  of  preadmission. 

SHAFT-GOVERNORS. 

A  paper  read  by  Mr.  Frank  H.  Ball  before  the  American  Society  of  Mechanical  Engineers  (see 
Transactions,  A.S.M.E.,  Vol.  XVIII,  page  290),  shows  three  forces  available  in  shaft-governor  con- 
struction, as  follows: — 

1.  Centrifugal  force  (Fig.  103). 

2.  Tangential  accelerating  force  (Fig.  104). 
'3.     Angular  accelerating  force  (Fig.  105). 

Each  of  the  Figs.  103,  104  and  105  represents  the  governor  wheel,  or  fly-wheel  to  which  the  gov- 
erning mechanism  is  attached,  a  is  the  shaft,  b  is  the  mass,  c  the  pivot  supporting  the  mass  through 
the  link  d. 

The  rotation  of  the  wheel  in  Fig.  103  will  cause  the  mass  b  to  move  outward  and  produce  centrif- 
ugal force. 

In  Fig.  104  the  mass  b,  being  connected  radially  to  the  pivot  c,  can  have  no  motion  due  to 
centrifugal  force.  On  account  of  its  inertia  it  will,  however,  move  relatively  in  the  direction 
shown  by  the  arrow  e  if  the  angular  velocity  of  the  wheel  increases,  or  in  the  direction  /  if  the  angular 

•f 


FIG.  103. 


FIG.  104. 


FIG.  105. 


velocity  of  the  wheel  decreases.  (Governors  using  this  force — -or  the  following  one,  or  both — are 
sometimes  termed  "inertia"  governors,  but  owing  to  the  forces  1,  2  and  3  being  combined  in  so  many 
different  ways  by  manufacturers,  we  will  not  speak  of  inertia  governors  as  a  class.)  This  force  is 
called  " tangential  accelerating  force." 

Angular  accelerating  force,  which  is  described  "as  the  effect  of  the  angular  acceleration  of  the 
mass  about  its  own  center  of  gravity,"  is  represented  in  Fig.  105,  in  which  the  mass  b  is  distributed. 

Effects  Produced  by  Rate  of  Rotation  and  by  Rate  of  Change  of  Rotation. 

To  distinguish  further  between  centrifugal  force  and  tangential  accelerating  force  (commonly 
called  "inertia"),  it  should  be  noted  that  the  former  depends  on  the  rate  of  rotation  only,  while  the 
latter  depends  entirely  on  the  rate  of  change  of  rotation. 


82 


The  "American  Electrician,"  in  the  early  part  of  1902,  illustrated  twenty-two  different  forms,  or 
makes,  of  the  shaft-governor,  all  making  use  of  centrifugal  force,  or  centrifugal  force  in  combination 

with  tangential  and  angular-accelerating  forces. 

THROTTLING  GOVERNORS. 

The  shaft-go vernor,|as  has  been  shown,\regulates  the  speed 
of  the  engine  by  changing  the  point  of  cut-off.  All  governors 
which  regulate  in  this  manner  may  be  placed  in  one  class,  and 
called  "  automatic  cut-off  governors. "  There  is  another  class 
of  governors  which  regulate  the  speed  of  the  engine  by  throt- 
tling, or,  in  other  words,  by  reducing  or  increasing  the  steam 
pressure  while  the  cut-off  remains  constant.  An  example  of 
this  latter  type  is  shown  in  Fig.  106,  which  is  an  illustration  of 
the  Pickering  governor.  A  belt  from  the  engine  shaft  drives 
the  pulley,  a,  and  this  rotation  is  carried  through  the  bevel 
wheels,  6  6,  to  the  three  weights,  c  c  c,  which  are  attached  to 
the  flat  springs,  d  d  d.  Should  the  engine  get  above  normal 
speed  the  weights,  ccc,  would  fly  out  by  centrifugal  force,  and 
in  so  doing  would  draw  down  the.  valves,  /  /,  through  the 
spindle,  e,  and  so  reduce  the  passage-way  for  live  steam  and 
consequently  the  steam  pressure,  g  is  live-steam  inlet,  and 
h  the  opening  to  the  steam  chest.  The  valves,  //,  are 
balanced,  the  steam  pressure  being  on  all  sides  alike.  The 
fly-balls,  ccc,  and  the  spindle,  e,  constitute  what  is  known 
as  the  revolving  pendulum. 

The  revolving  pendulum  is  also  applied  as  a  governor 
for  changing  the  point  of  cut-off,  as  used  on  the  Corliss  and 
other  engines  and  illustrated  in  Fig.  69,  in  which  a  is  a  pulley 
operated  by  a  belt  from  the  engine  shaft.  The  rotation  is 

carried  to  the  two  fly-balls,  c'  c',  through  a  spindle  in  the  post  6.  As  the  engine  speeds  up  above 
normal  the  balls,  c'  c',  fly  out  and  turn  the  rocker  ef  through  a  rod  in  the  post  b  and  an  arm  (er  d) 
which  is  securely  fastened  to  the  rock-shaft  d.  The  governor-rods  g  and  h  are  attached  to  knock- 
off  cams  which,  by  their  rotation,  regulate  the  point  of  cut-off,  as  shown  in  the  explanation  of  the 
Corliss  valve-gear. 

DRAFTING-TABLE  PROBLEM,  No.  6 — COMPARING  RESULTS  FROM  STRAIGHT-SLOT  AND  ROTATING 

ECCENTRICS. 

Construction  of  Comparative  Indicator  Cards:  One  Obtained  from  an  Eccentric  having  a  Straight  Slot,  which  gives 
a  Constant  Lead  with  a  Variable  Travel  and  Angle  of  Advance;  the  Other  Obtained  by  Rotating  an  Ordinary  Eccen- 
tric, which  gives  a  constant  travel  with  a  Variable  Lead  and  Angle  of  Advance. 

A  comparison  of  the  results  obtained  by  the  use  of  the  two  kinds  of  eccentrics  mentioned  in 
this  problem  may  be  shown  to  best  advantage  by  assuming  a  concrete  example  in  which  both 
eccentrics  are  designed  to  cut-off  at  a  given  point  in  the  stroke,  and  then  moving  each  so  as  to 
produce  cut-off  at  an  earlier  point  in  the  stroke. 

To  facilitate  the  work  the  student  may  refer  to  the  Zeuner  diagram  of  Problem  1,  in  which 
a  plain  slide-valve  was  designed  to  obtain  cut-off  as  given  above.  Construct  the  indicator  card 


FIG.  106. 


83 

for  the  head  end  for  this  case,  using  a  live-steam  pressure  of  80  Ibs.  gauge,  with  2  Ibs.  back  pressure 
and  a  40  spring.  Assume  a  clearance  volume  of  5  per  cent. 

In  Fig.  107  the  dotted  construction  work  is  taken  from  the  Zeuner  diagram  of  Problem  1,  C  0 
representing  the  crank  position  for  the  given  cut-off,  D  K  L  the  steam-lap  circle,  G  F  the  lead, 
and  D  E  F  the  Zeuner  circle. 

To  construct  the  Zeuner  diagram  for  the  rotating  eccentric  for  any  other  cut-off,  such  as  at 
0  J,  draw  K  At  perpendicular  to  0  J,  and  the  arc  N  E  P  with  0  E  as  a  radius.  The  intersection 


ANY  ASSUMED 
EARLIER  CUT- OFF. 


FIG.  107. 

of  K  M  with  this  arc  gives  the  point  R,  the  extremity  of  the  diameter  of  the  Zeuner  circle  for  cut- 
off at  0  J. 

To  obtain  the  Zeuner  diagram  for  the  straight-slot  eccentric  for  cut-off  at  0  J,  for  example, 
locate  the  point  S  at  the  intersection  of  KM  with  E  F,  E  F  being  the  line  of  constant  lead.  Then 
0  S  equals  the  diameter  of  the  Zeuner  circle  for  the  straight-slot  eccentric  cutting,  off  at  0  J. 

In  the  diagram  for  this  problem,  draw  in  the  symmetrically  situated  Zeuner  circles  for  the 
complete  revolution,  and  locate  and  designate  the  piston  positions  for  all  events  of  the  stroke. 
Enter  the  results  in  a  table  as  follows : 


84 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


Method 
of 
governing 

Angle 
of 
advance 

Travel 
of 
valve 

Lead 

Per  Cent,  of  Stroke  Completed  When 

Admission 
begins 

Cut-off 
takes 
place 

Release 
begins 

Compres- 
sion begins 

Both  eccen- 
trics at  

/ 

cut-off 

Rotating 
eccentric  at 
...CO. 

Straight-slot 
eccentric  at 
.  .  .  cut-off. 

SECTION   V.— VALVE-GEARS. 

Link-motions  are  extensively  used  in  engines  where  reversals  in  the  direction  of  running,  var- 
iable speeds,  etc.,  are  required.     This  occurs  chiefly  in  locomotives,  marine  engines,  rolling  mill 


I ~ Full  Gear  Forward. 

5~   •         •<     Bac-knard. 

S  -Mill       - 

L-lnhrmedigte  Gear  Ftrward. 

•*-  -     Backward. 


'0 


FIG.  1C8. 


engines,  etc.     Perhaps  the  most  largely  used  of  all  the  link-motions  is  the  Stephenson,  shown  in 
Fig.  108,  which  represents,  in  a  diagrammatic  manner,  its  application  to  the  locomotive. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  85 

STEPHENSON  GEAR. 

The  explanation  of  the  action,  in  a  general  way,  is  as  follows:  For  the  position  shown,  the 
valve  is  being  operated,  through  the  rocker,  by  means  of  the  forward  eccentric  only.  This  is  evi- 
dent from  the  fact  that  the  slide-block,  which  is  pivoted  to  the  end  of  the  rocker-arm,  is  in  direct 
line  with  the  forward  eccentric-rod;  in  this  position  the  backing  eccentric-rod  has  no  influence 
on  the  valve  motion. 

If,  now,  the  reversing-lever  be  moved  so  as  to  clasp  in  notch  2,  the  linkj  through  the  revers- 
ing-rod,  bell-crank  and  hanger,  will  be  raised  so  that  the  saddle-block  pin  is  closer  to  the  slide- 
block  pin.  The 'slide-block,  which  will  then  have  a  motion  due  to  both  eccentric-rods,  will  have 
a  shorter  horizontal  swing,  and  the  valve  consequently  will  have  less  travel,  less  port-opening, 
earlier  cut-off,  and  will  furnish  less  power  to  the  engine. 

With  the  reversing  lever  in  its  central  position,  or  notch  3,  the  saddle-block  pin  and  the  slide- 
block  pin  will  be  over  each  other,  and  the  travel  of  the  valve  and  port  opening  'will  be  a  minimum. 

Method  of  Reversing. 

The  link  and  the  connections  are  so  designed  that  when  the  reversing-lever  is  moved  to  notch 
5  the  backing  eccentric-rod  is  raised  so  as  to  be  in  line  with  the  slide-block  pin,  which  is  thus  drawn 
to  one  side  or  the  other,  except  when  the  engine  is  on  dead-center.  This  causes  the  rocker  to  turn 
on  its  shaft,  and  move  the  valve  to  the  right  or  left  to  such  an  extent  that  the  opposite  port  may 
open  to  steam  and  reverse  the  engine.  When  the  engine  is  on  dead-center  the  slide-block  and 
valve  will  remain  nearly  stationary  when  the  link  is  raised  or  lowered  and  the  cylinder  on  the  oppo- 
site side  of  the  locomotive  with  its  crank  at  90°  must  be  relied  upon  to  start  up. 

A  Valve-Gear  at  any  One  Setting  Equivalent  to  an  Eccentric. 

The  link,  operated  by  two  fixed  eccentrics,  is  for  any  one  phase  or  notch  setting,  a  mechanical 
equivalent  for  a  single  curved-slot  eccentric.  Such  an  equivalent  eccentric  is  sometimes  called  a 
virtual  eccentric.  The  link,  however,  has  an  advantage  over  the  latter,  in  that  it  is  capable  of  such 
adjustment  that  practically  nullifies  the  irregularity  of  cut-off  and  exhaust  closure  due  to  the  angu- 
larity of  the  connecting-rod. 

A  more  definite  idea  of  the  complex  action  of  the  link  and  its  connecting  mechanisms  is  shown 
in  a  graphical  manner  by  the  method  given  by  Auchincloss,  as  illustrated  in  Figs.  109,  110  and  111. 
Fig.  109  is  a  center-line  reproduction  of  Fig.  108,  the  line  o  s  r  o  of  the  template,  in  Fig.  109,  corre- 
sponding to  the  center-line  o  s  r  o  of  the  link  in  Fig.  108. 

In  Fig.  110  the  lines  00,  11,  22,  etc.,  represent  the  successive  positions  of  the  center-line  o  s  r  o 
of  the  link  during  one  cycle.  The  curves  u  v  and  w  x,  which  are  envelopes  of  the  link  center-lines 
of  Fig.  110,  are  reproduced  for  clearness  in  Fig.  111.  The  length  of  the  horizontal  line  included 
between  these  two  curves  measures  the  limits  of  the  horizontal  travel  of  the  link.  For  example, 
if  the  slide-block  pin  is  at  h  the  valve-travel  is  y  z,  and  the  travel  of  the  saddle-block  pin  is  p  t. 

Detail  Construction. 

Briefly,  the  order  of  construction  for  the  illustrations  thus  far  referred  to  is  as  follows,  keeping  in 
mind  that  all  that  is  shown  in  Figs.  109,  110  and  111  should  be  developed  step  by  step  on  one  single 
figure.  The  figures  are  separated  here  to  avoid  complication  of  line  work. 

In  Fig.  109  take  o'  for  the  shaft  center  and  o'  c  for  the  crank  on  dead-center.  Lay  off  points  a  and 
b  (according  to  the  angle  of  advance)  as  the  eccentric-center  positions  for  crank  at  o'  c,  and  draw  the 
eccentric-center  circle.  With  the  length  of  the  eccentric-rods  (a  m  and  6  n)  and  the  dimensions  of 


86 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


the  link  template  (m  n,  m  r  and  n  s)  given,  the  eccentric-rods  and  template  may  be  drawn  in  position 
as  shown  for  the  engine  on  dead-center.  Then  taking  the  lap  plus  lead  from  the  angle  of  advance  at 
a,  lay  it  off  from  the  template  edge  at  r  to  h.  From  h  draw  the  vertical  line  and  on  it  lay  off  the 
given  distance  from  h  to  g  (the  rock-shaft  center).  The  line  h  g  is  then  the  position  of  the  rocker 


FIG.  109. 


FIG.  110. 


FIG.  111. 


when  the  valve  is  central,  and  g  r  is  the  position  of  the  rocker-arm  after  the  valve  has  moved  off 
center  a  distance  equal  to  the  lap  plus  the  lead.  (This  position  is  represented  in  Fig.  108,  where 
the  small  port-opening  shown  represents  .the  lead.  It  will  be  noted  that  the  crank  o  c  is  on  dead- 
center,  as  it  should  be  for  this  position  of  the  valve.) 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


87 


Lay  off  r  I  =  lead;  then  h  I  is  the  lap.  For  illustration,  assume  the  lap  to  be  %  (lap  +  lead). 
Then  with  the  center-line  of  the  rocker-arm  at  g  I  the  valve  will  have  moved  a  distance  off  center 
equal  only  to  the  lap,  and  admission  will  have  begun. 

The  next  step  in  the  layout  of  a  problem  by  this  method  consists  in  cutting  a  template  of  some 
suitable  material,  with  the  center-line  o  r  s  o  of  the  link  as  its  right-hand  bounding  line,  and  with 
notches  at  m,  n  and  q  corresponding  to  the  two  eccentric-rod  pin  points  and  the  saddle-block  pin 
point.  This  latter  point  must  always  lie  on  the  arc  q'  q  q"  described  about  /  as  a  center,  and  the 
points  m  and  n  must  always  lie  on  arcs  described  with  the  eccentric-rods  as  radii  in  their  successive 
positions.  .  The  exact  location  of  /  depends  on  frame-work  construction,  and  in  this  problem  may  be 
assumed  approximately  as  shown.  The  lines  on  which  m  and  n  must  always  be  found  are  obtained 
as  follows:  Divide  the  eccentric  circle,  Fig.  110,  into  a  convenient  and  sufficient  number  of  parts  de- 
pending upon  the  accuracy  required — six  are  shown  in  this  case.  These  divisions  are  laid  off  in  the 
direction  of  rotation,  first  from  a,  for  the  forward  eccentric,  and  then  from  6  for  the  backing  eccentric. 
From  each  of  these  division  points,  draw  the  arcs,  la  ,  2a,  and  16,  26,  etc.,  using  the  eccentric-rod 
length  as  a  radius.  These  arcs  will  contain  the  points  m  and  n  of  the  template  in  its  successive  posi- 


C     0 


FIG.  112. 


FIG.  113. 


tions  and  in  addition  the  point  q  of  the  template  must  always  lie  on  the  arc  q'  q  q".  The  template 
may  now  be  adjusted  for  the  six  positions,  thus  giving  the  lines  0  0,  1  1,  2  2,  3  3,  4  4  and  5  5  in  Fig. 
110.  Draw  envelopes  to  these  curves  as  shown  at  w  x  and  u  v. 

In  Fig.  Ill  these  envelopes  are  reproduced.  Draw  the  arc  h  i  with  a  radius  o'  h.  With  h  as  a 
center  draw  the  lap,  and  lap  +  lead  circles,  with  h  I  and  h  k  as  radii,  respectively.  Draw  similar 
circles  at  m.  Then  with  o'  as  a  center  draw  the  arcs  I  m  and  I'  m';  the  travel  of  the  slide-block  pin, 
from  the  center  arc  h  i  to  /  m  or  to  I'  m'  is,  approximately,  just  sufficient  to  take  up  the  outside  lap 
of  the  valve.  Draw  a  curve  tangent  to  the  lap  +  lead  circles  at  the  top  and  bottom,  and  also  tangent 
to  the  envelopes  at  p  and  t;  the  travel  of  the  slide-block  pin  between  the  two  curves  h  i  and  k  t  is 
just  sufficient  to  move  the  valve  a  distance  equal  to  the  lap  plus  the  lead.  It  will  be  seen  that  the 
lead  will  vary  with  the  different  elevations  of  the  link.  The  distance  from  I'  m'  to  w  x  is  the  port- 
opening. 

"Slip." 

In  the  practical  adjustment  of  the  link  and  its  connecting  mechanism  for  precise  work,  one  great 
difficulty  arises  on  account  of  the  "slip"  which  occurs  between  the  slide-block  and  the  link.  This 
slip  is  shown  in  Fig.  110  as  follows : 

The  upper  dotted  loop  shows  the  path  of  the  point  r  on  the  surface  of  the  link  during  one  revolu- 


88 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


tion  of  the  crank.    A  corresponding  point  of  the  surface  of  the  slide-block  can  only  travel  in  the  arc 
h'  h  h"  about  g.    It  will  be  seen  therefore  that  slip  during  one  revolution  equals  the  distance  s. 

In  planning  a  link  motion  it  is  necessary  to  reduce  this  slip  as  much  as  possible,  on  account  of 
wear.  When  the  link  is  in  such  a  position  that  the  saddle-pin  is  directly  over  the  slide-block  pin, 
the  slip  is  comparatively  small. 

Open  and  Crossed  Rods. 

Links  may  be  connected  with  the  eccentrics  in  two  different  ways,  either  by  "open  rods,"  as 
shown  in  Fig.  112,  or  by  "closed"  or  "crossed"  rods,  as  shown  in  Fig.  113.  When  the  centers  of  the 
two  eccentrics  (a  and  6)  lie  between  the  shaft  and  the  link,  and  the  projections  of  the  rods  do  not 
intersect,  the  rods  are  said  to  be  "open."  When  the  eccentric-centers  lie  between  the  shaft  and  the 
link,  and  the  projection  of  the  rods  cross  each  other,  the  rods  are  said  to  be  "  crossed. "  It  should  be 
noted  that  the  position  of  the  crank  has  nothing  whatever  to  do  with  open  or  crossed  rods. 


FIG.  114. 


Other  things  being  equal,  open  and  crossed  eccentric-rods  give'quite  different  steam"distributions. 
In  Fig.  114  the  link  is  shown  in  position  1  in  full-gear,  and  in  position  2  in  mid-gear,  jffltjwill^be  seen 
that  the  lead  for  full-gear  is  d  e,  and  that  for  mid-gear  it  is  —ef.  In^other  words,  the  lead^decreases 
from  full  to  mid-gear,  even  to  negative  lead  sometimes,  as  shown  in  this  case,  with  crossed  rods. 
With  open  rods  the  lead  increases  from  full  to  mid-gear,  being  shown  equal  ioj  k  for  full,  and  equal 
to  j  I  for  mid-gear,  in  Fig.  115.  The  effect  of  short  open  rods  is  to  increase  the  lead  more  rapidly,  as 
also  shown  in  Fig.  115,  where  m  p  is  greater  than .;'  I. 

Inasmuch  as  the  half-travel  of  the  valve  in  mid-gear  is  equal  only  to  the  lap  +  lead  (Fig.  Ill),  and 
if  the  lead  for  mid-gear  is  zero,  or  a  minus  quantity  (as  represented  in  Fig.  114),  it  will  be  observed 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


89 


that  the  half-travel  of  the  valve  is  equal  to,  or  less  than,  the  lap  of  the  valve  in  crossed  rods;  in 
which  cases  steam  will  not  be  admitted  to  the  cylinder.  Therefore,  in  a  crossed-rod  design  where  the 
lead  at  full-gear  is  small  enough,  it  is  possible  to  shut  off  steam  by  placing  the  link  in  mid-gear.  With 
open-rods  this  cannot  be  done,  no  matter  how  small  the  full-gear  lead  for  the  reason  that,  as  has  been 
stated,  the  lead  increases  from  full  to  mid-gear,  and  therefore  the  steam-ports  are  open  a  definite 
amount  for  every  setting  of  the  link  when  the  engine  is  in  dead-center.  In  practice,  generally,  open- 
rods  are  used,  and  the  lead  for  mid-gear  position  r'anges  from  J4  inch  to  Y%  inch  with  a  common  value 
%  inch,  while  the  full-gear  lead  ranges  from  %,  inch  to  %  inch,  governed  principally  by  the  length  of 
the  eccentric-rod. 

Several  practical  considerations  in  connection  with  link  mechanism  should  be  pointed  out : 
1.     That  the  bell-crank  shaft  must  be  situated  a  sufficient  distance  above  or  below  the  center- 
line  of  motion  so  that  the  eccentric-rods  do  not  strike  it  when  raised  or  lowered  to  full-gear. 


FIG.  115. 


2.     The  hanger  should  be  of  such  length  that  the  link  will  not  conflict  with  the  bell-crank  in  any 
position.     The  length  of  the  bell-crank  arm  is  usually  equal  to,  or  greater  than,  the  hanger. 


Relation  Between  Center-Lines  of  Valve-Gear  and  Engine  Cylinder. 

3.  So  long  as  the  angular  advance  of  the  eccentric  is  laid  off  from  a  line  at  right  angles  to  the 
central  line  of  the  link-motion,  the  latter  may  be  arranged  to  any  inclination  to  the  piston  motion 
without  affecting  the  action  of  the  link.  In  Fig.  108  the  center-lines  of  the  link-motion  and  the  piston- 
motion  coincide.  With  proper  mechanical  connections  the  valve  motion  would  remain  the  same  if 
the  link,  eccentric-rods,  and  eccentric-sheaves  were  considered  rigid  with  respect  to  each  other  while 
they  were  turned  through  any  desired  angle  about  0  as  a  center,  the  center-line  of  the  engine  remain- 
ing fixed. 


90 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


DESIGN  OF  A  STEPHENSON  GEAR. 

In  order  to  make  a  direct  and  practical  application  of  the  method  involved  in  laying  out  a  link- 
motion  for  an  actual  case,  let  the  following  data  be  given: 
Ratio  of  crank  to  connecting-rod  =  1: 7^. 
Eccentric  circle  diameter  =  5%  inches. 
Maximum  cut-off  =  0.92  stroke. 

Center  to  center  of  eccentric-pins  (m  to  n  of  Fig.  109)  =  13  inches. 
Center  of  eccentric-pin  back  of  link-arc  (mk  and  ns,  Fig.  109)  =3  inches. 
Mid-gear  lead  =  %  inch. 
Length  of  hanger  =18  inches. 
Exercise  Problem:  Find  the  steam-lap,  full-gear  lead,  point  of  suspension  of  link,  and  location  of  tumbling-shaft. 

The  mid-gear  lead  is  given  in  this  problem  for  the  reason  that  the  valve-travel  is  least  at  mid- 
gear,  as  may  be  seen  in  Figs.  110  or  111,  and  the  lead  therefore  constitutes  a  much  larger  percentage 
of  the  steam-port  opening  near  mid-gear  than  it  does  in  full-gear.  In  fact  at  mid-gear  the  lead  and 
steam-port  opening  are  the  same. 

In  designing  link-motions  for  actual  service  it  must  be  kept  in  mind  that  the  work  cannot  be 
carried  out  from  start  to  finish  with  mathematical  precision,  but  that  approximations  must  be  made 
in  several  of  the  steps,  and  finally,  adjustments  made  to  secure  the  desired  results. 

To  Find  Mid-Gear  Travel. 

The  first  step  in  the  design  will  be  to  find  the  mid-gear  travel  of  the  valve  for  the  assigned  con- 
ditions. Special  directions  for  doing  this  will  be  found  in  the  succeeding  paragraph,  the  general 
plan  being  to  lay  off  the  eccentric-centers  F  and  B,  Fig.  116,  for  the  forward  and  backing  eccentrics 


FIG.  116. 


(for  a  92%  cut-off)  when  the  piston  is  at  one  end  of  the  stroke,  and  /  and  b  likewise  when  the  piston 
is  at  the  other  end  of  the  stroke.  Then,  taking  the  eccentric-rod  lengths  and  a  template  (such  as 
in  Fig.  118)  whose  edge  coincides  with  the  center-line  curve  of  the  link,  the  extreme  positions  of 
the  link-arcs  y  z  and  yi  Zi,  Fig.  117,  may  be  found  by  placing  the  eccentric-centers  at  F  and  B, 
and  /  and  6,  respectively,  thus*  giving  di  d^  as  the  travel  in  mid-gear. 

In  following  this  plan  the  student  may  need  to  refer  to  the  following  directions  as  to  detail: 
Figs.  116  and  117  are  connected,  the  distance  from  the  point  F  in  Fig.  116  to  the  arc  F  in  Fig.  117 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  91 

being  equal  to  the  length  of  the   eccentric-rod,  which  is  46  J4  inches  (49^"  —  3").     The   angle 

G  C  F  is  the  angle  of  advance  for  92%  cut-off,  and  is  found  to  be  equal  to  about  17°  for  this  problem.* 

The  student  should  note  and  understand  that  on  account  of  the  reversing-rocker  which  is  used 


FIG.  119. 

with  the  Stephenson  link,  the  eccentric  must  follow  instead  of  precede  the  crank,  and  that  the 
actual  angle  of  advance  must  be  laid  off  back  of  90°  instead  of  in  advance  of  it. 

*The  reason  for  connecting  17°  angular  advance  with  92%  cut-off  maybe  explained  by  the  following  independent 
example  according  to  explanation  on  pages  3  and  4:  Given  the  crank  a  c,  Fig.  119,  and  the  eccentric  a  b  with  an  angle 
of  advance  of  20°.  If  we  neglect  lead,  and  give  the  valve  a  steam-lap  equal  to  b  d,  the  steam-port  will  just  be  opening 
at  the  crank  position  shown.  When  the  eccentric  a  b  gets  to  af,  which  also  makes  an  angle  of  20°  with  a  h,  the  steam- 
port  is  just  closing  and  the  eccentric  has  traveled  140°.  The  eccentric  and  crank  being  rigidly  connected,  the  latter 
has  also  traveled  140°  when  cut-off  takes  place.  If,  therefore,  the  position  of  the  crank  at  cut-off  is  given  in  a  problem, 
asTiO0,  foFexample,  it  may  be  shown  that  the  angle  of  advance  necessary  to  secure  this  equals  Yt  (180°  —  140°)  -  20°, 
if  lead  is  neglected.  If  the  lead  angle  is  taken  into  account,  and  is,  say,  10°,  as  shown  at  b  a  k,  Fig.  119,  then  the  cut- 
off will  occur  10°  sooner  with  the  same  lap,  or  at  130°,  as  may  be  seen  by  a  study  of  Fig.  119.  There  being  no  revers- 
ing-rocker  in  this  explanation,  the  eccentric  precedes  the  crank,  and  the  angle  of  advance  is  laid  off  ahead  of  90°. 


92  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

As  the  whole  design  is  approximate,  and  the  full-gear  lead  smaller  than  %  "  but  not  yet  definitely 
known,  it  may  be  neglected  in  laying  out  the  eccentric  positions  F  and  B  in  Fig.  116  (for  the  crank 
at  C  D)  and  /  and  6  (for  the  crank  at  C  E) 

Since  the  eccentric-rod  pins  are  3  inches  back  of  the  link-arc,  the  eccentric-rod  itself  is  4934 
inches  —  3  inches  or  4634  inches  long.  With  this  as  a  radius  strike  the  arcs  F,  B,  f,  b,  of  Fig.  117, 
with  the  corresponding  points  of  Fig.  116  as  centers.  Then  construct  a  template  having  a  link- 
arc  of  49)4  inches  radius,  and  with  incisions  as  shown  at  m  and  n  of  Fig.  118, 13  inches  apart  and  3 
inches  back  of  the  link-arc.  Mark  the  point  j  midway  between  m  and  n.  Then  adjust  the  tem- 
plate on  the  arcs  F  and  B,  Fig.  112,  and  draw  the  link-arc  position  y  z  for  mid-gear.  Similarly 
with  the  arcs  /  and  b  find  the  link-arc  position  yi  z, .  With  the  template  in  this  position  draw  j  r, 
Fig.  118,  coincident  with  the  central  line  of  motion  C  A.  Also  draw  m  y'  and  n  z'  parallel  to  j  r. 
The  arcs  y  z  and  yi  Zi  cross  the  center-line  of  motion  at  d,  and  dt,  which  therefore  measure  the  valve- 
travel  at  mid-gear.  The  point  A,  midway  between  di  and  d,  determines  the  location  of  the  rocker- 
shaft.  It  should  be  observed  that  the  distance  C  A  is  now  slightly  more  than  the  assigned  value 
of  4934  inches,  due  to  the  curvature  of  the  link-arc.  This  increase,  however,  is  neglected  in  practice, 
and  A  R  is  taken  as  the  position  of  the  rocker-arm  when  the  valve  is  central. 

To  Find  the  Lap  of  the  Valve. 

From  di  and  d2,  Fig.  117,  lay  off  the  given  mid-gear  lead  of  Y%  inch  equal  to  di  I  and  d,  It,  and 
draw  the  circles  I  lt  and  d,  d,.  A  Us  the  steam-lap,  I  di  the  lead  and  A  di  the  half-travel  for  mid- 
gear. 

To  Find  Position  of  Center  of  Saddle-Pin  for  Equalized  Cut-Off  at  Half  Stroke. 

The  location  of  the  saddle-pin  center  is  perhaps  the  most  important  feature  in  the  design  of 
a  link-motion,  and  should  be  carefully  selected.  By  a  proper  determination  of  its  location  the  cut- 
off on  the  two  ends  of  the  cylinder  may  be  practically  equalized  for  any  single  point  in  the  stroke. 

Inasmuch  as  the  inequality  due  to  the  crank  angles  is  greatest  at  about  Yi  stroke,  the  irregu- 
larity of  cut-off  will  be  greatest  for  this  position  unless  corrected.  This  design  will  therefore  be 
laid  out  to  give  equal  cut-offs  at  one-half  the  stroke  on  each  end  of  the  cylinder,  with  a  symmetrical 
valve. 

When  the  piston  is  at  Yi  stroke  the  crank-pin  D,  Fig.  116,  will  have  advanced  a  little  less  than 
90°  forward  stroke,  and  a  little  more  than  90°  on  the  return  stroke,  and  the  eccentric-centers  F 
and  B  will  have  advanced  correspondingly.  Find  these  two  angles,  and  lay  the  forward  one  off 
from  F  and  B,  thus  obtaining  Yi  /  and  Yi  6,  and  the  return-stroke  angle  from  /  and  6  which  will 
give  the  points  /  Yi  and  b  Yi-  With  the  four  points  just  found,  as  centers,  and  with  a  radius  equal 
to  the  eccentric-rod  length  (4634  inches),  describe  the  arcs  3^/,  Yi  b,  f  3/2  and  6  Yii  Fig.  117.  Adjust 
the  template  with  m  and  n  on  the  arcs  }/£  /  and  Yi  b,  respectively,  and  with  the  link-arc  passing 
through  I.  This  will  give  the  position  (l/%  y,  Yi  2)  f°r  the  link-arc  for  ^  cut-off  in  the  forward 
stroke.  Mark  the  position  of  j  r  of  the  template  at  Y%  j>  Yi  f  on  the  diagram.  In  a  similar  man- 
ner yYt,zYi  and  jYiirYi  niay  be  found  for  the  position  of  the  link-arc  for  3^  cut-off  on  the  return 
stroke.  The  link  is  now  shown  in  the  two  positions  for  equalized  cut-off,  and  inasmuch  as  the 
point  of  suspension  in  locomotive  practice  is  usually  at  the  center  of  the  link,  the  saddle-pin  center 
must  be  found  on  the  lines  Yi  j>  Yi  r,  and  j  Y%,  r  Yi-  It  must,  of  course,  be  the  same  distance  from 
the  link-arc  in  each  position.  Therefore,  locate  the  two  points  s  and  sl  at  equal  distances  from 
Yi  f  and  r  Yi)  respectively,  and  of  such  length  that  a  line  c  c  parallel  to  the  central  line  of  motion 
may  be  drawn  through  them.  This  line  represents  the  path  of  the  travel  of  the  saddle-block  pin, 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


93 


and  is  in  reality  an  arc  with  the  hanger  as  the  radius.  For  the  short  distance  s  s,  it  may  be  con- 
sidered a  straight  line.  Having  determined  the  point  of  suspension  of  the  link  make  the  incision 
s  on  the  template.  (See  Fig.  118.) 

To  Locate  the  Bell-Crank  or  Tumbling-Shaft  for  Equalized  Cut-Off  at  All  Points  of  Stroke. 

The  cut-off  has  now  been  equalized  for  %  stroke  where  the  inequality  due  to  the  connecting- 
rod  angles  is  naturally  at  its  maximum.  The  influence  of  this  inequality  becomes  less  and  less 
as  the  cut-off  grows  later,  and  therefore  if  the  maximum  desired  cut-off  (in  this  case  0.92  stroke) 
be  equalized,  all  intermediate  cut-off  positions  between  mid  and  full-gears  will  practically  be 


FIG.  120. 


Z092 


FIG.  121. 

equalized.     This  may  be  accomplished  by  working  out  the  proper  location  of  the  tumbling-shaft 
T,  Fig.  121. 

Figs.  116  and  117  might  be  used  for  this  work,  but  it  would  complicate  the  diagrams  too  much. 
Therefore,,  on  a  new  diagram  lay  off  F,  B,  f  and  6  with  the  same  values  as  before;  and  find  positions 
0.92  /,  0.92  b,  f  0.92  and  6  0.92,  Fig.  120,  for  the  eccentric  centers  when  the  piston  has  traveled  0.92 
of  its  stroke,  in  the  same  manner  as  %  /,  ^  b,  etc.,  were  found  for  J/£  stroke.  Then  with  the  same 
eccentric-rod  radius  as  before,  describe  the  arcs  0.92  /,  0.92  b,  f  0.92  and  b  0.92  in  Fig.  121.  Adjust 
the  template  so  that  m  and  n  fall  on  the  arcs  0.92  /  and  0.92  6,  and  the  link-arc  passes  through  I. 
Draw  the  arc  0.92  y  0.92  z  and  mark  the  point  sa  through  the  point  s  on  the  template.  This,  then, 


94 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


is  the  position  for  the  link  at  0.92  cut-off  running  forward.  Do  the  same  for  0.92  cut-off  on  the 
return  stroke,  and  mark  the  position  s3.  Join  s2  and  ss  by  a  straight  line  ci  ci,  which  will  be  found 
to  have  a  slight  inclination  to  the  central  line  of  motion,  but  too  small  to  produce  much  ill  effect, 
It  could  be  made  parallel  by  placing  sa  and  s3  nearer  the  link-arc,  but  this  would  destroy  the  equality 
of  cut-off  at  ^  stroke. 

The  saddle-pin  locations  s4  s6  and  s6  s,  for  equal  cut-offs  in  back-gear  could  be  found  if  neces- 
sary, but  in  most  locomotive  work  the  back-gear  is  a  counterpart  of  the  forward-gear,  and  these 
points  may  consequently  be  placed  symmetrically  with  respect  to  s  si  and  sa  s3. 


/? 


/, 

•/  +, 


LAP 


PORT  OPENING 

?  WLVE  TRAVEL 


ffOCK  SHAFT  ARC 


y4 


^ 


d\  /*r,~~-.y^  SLIP 


\/ 


•d< 


/I 


FIG.  122. 


Having  determined  the  stud  positions  for  equalized  50%  and  92%  cut-offs,  it  only  remains  to 
suspend  the  hanger  in  such  manner  that  for  the  several  elevations  its  opposite  end  will  sweep  through 
the  corresponding  positions  of  s,  Si  sa,  sa  etc.  With  an  assumed  length  of  hanger  (which  is  usually 
determined  by  the  space  available)  as  a  radius,  and  with  s2  s3  as  centers,  strike  arcs  intersecting 
at  h.  In  a  similar  manner,  with  the  other  three  sets  of  points,  obtain  hi,  ht  and  h3.  These  points 
will  not  fall  on  the  arc  of  any  circle,  but  an  approximate  one  may  be  found  which  will  give  a  center 
at  T,  and  this  point  will  be  the  center  for  the  bell-crank  shaft. 


95 


To  Find  the  Lead  on  the  Forward  and  Return  Strokes  in  Full-Gear. 

With  the  points  F,  B,  f  and  6  sweep  arcs  F,  B,  f  and  b  on  a  new  diagram  (not  shown  here)  similar 
to  those  in  Fig.  117,  and  adjust  the  template  with  m  and  nonF  and  B,  and  with  s  on  c,  Ci  of  Fig.  121 . 
Mark  the  point  in  which  the  link-arc  intersects  the  line  of  motion.  (Figs.  120  and  121  are  necessarily 
drawn  on  such  a  small  scale  that  instead  of  further  complicating  these  figures  by  drawing  in  this  con- 


o 


o 


o 


FIG.  124. 


FIG.  125. 


FIG.  123. 

struction  we  will  show  the  results  of  the  construction  called  for  in  this  paragraph  in  the  separate  Fig. 
122.)  The  distance  of  this  point  to  A,  minus  A  I,  will  be  the  lead  (equal  I  d)  at  full-gear  on  the  for- 
ward stroke.  In  the  same  manner,  by  using  arcs  /  and  6,  the  lead  on  the  return  stroke  full-gear 
may  be  obtained  equal  to  li  d3.  These  leads  (I  d  and  L  d,)  will  be  found  to  be  slightly  unequal,  but 
on  account  of  the  large  port-opening  at  full-gear,  the  effect  of  their  inequality  may  be  neglected. 

To  Find  Extreme  Travel  of  the  Link  and  the  Slip. 

With  the  template  in  position  on  the  arcs/  and  b  as  called  for  in  the  previous  paragraph,  the  point 
y'  (Fig.  118)  on  the  link-arc  will  have  its  greatest  elevation  for  full-running  position,  as  represented  at 


96 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


7/3  23  in  Fig.  122.  The  forward  eccentric  has  its  greatest  throw  when  .F  is  at  D,  Fig.  120,  then  B  is  to 
the  left  an  amount  corresponding  to  the  arc  F  D,  and  the  link  is  in  its  greatest  inclined  position,  as 
represented  by  the  link-arc  yt  z4  in  Fig.  122.  For  this  position  the  point  p  of  the  link-arc  is  on  the 
rock-shaft  arc,  and  is  the  distance  p  i/4  from  y'  on  the  template.  For  position  y3  z3  the  point  d3  of  the 
link-arc  is  on  the  rock-shaft  arc.  The  maximum  slip  is  therefore  p  dt. 

For  further  reference  in  laying  out  this  link-motion  graphically,  see  "Link  and  Valve  Motions/' 
by  Auchincloss,  pages  90  to  135. 

Use  of  Models  in  Construction  of  Valve-Gears. 
Models  are  sometimes  built,  and  the  required  valve  motion  obtained  by  adjustments  in  the 

several  parts  of  the  model. 

LINKS. 

Classifications  and  Types. 
Links,  in  general,  may  be  classified  in  two  independent  ways: 

1.  With  reference  to  their  suspension,  into  ''shifting"  and  "stationary"  links. 

2.  With  reference  to  their  form,  in  which  we  have  the  "box"  link,  Fig.  123;  the  "open"  link, 


J 

cm 


H 


K 


o 


a° 


D 


FIG.  126. — Stephenson  Double-Bar  Link. 

solid,  Fig.  124;  the  "open"  link,  built  up,  and  more  generally  known  as  the  "skeleton"  link,  P'ig. 
125,  and  the  "double-bar"  link,  Fig.  126. 

Shifting  and  Stationary  Links. 

The  "shifting"  link  is  represented  in  the  Stephenson  gear,  Fig.  108;  the  "stationary"  link  in  the 
Gooch  gear,  Fig.  129.    A  "shifting"  link  is  distinguished  by  the  fact  that  the  link  itself  is  moved  up  or 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


97 


down  to  secure  variable  cut-off  or  reversal;  in  the  "stationary"  link  the  "radius-rod"  instead  of  the 
link  is  moved  to  secure  variable  cut-off  or  reversal.  Both  the  shifting  and  stationary  links  have 
similar  motions  throughout  a  cycle. 

Forms  of  Links  in  General  Use. 

The  forms  of  links  most  used  in  American  practice  are  shown  in  Figs.  124,  125  and  126.     In  the 
link  shown  in  Fig.  124  the  eccentric-rod  pins  may  be  placed  on  extensions  of  the  link-arc  a  c,  in  which 


FIG.  127. — Arrangement  of  Stephenson  Link  and  Rock-Shaft  Connections. 

case  the  diameter  of  the  eccentric  circle  must  be  greater  than  the  travel  of  the  valve.  The  "double- 
bar"  link,  as  shown  in  Fig.  126,  is  applied  principally  to  marine  engines;  its  action  is  shown  in  Fig. 
127,  in  which  L  is  the  link,  P  and  Q  the  eccentric-rods,  M  side  or  bridle-rods,  N  the  rock-shaft  arm, 
0  the  rock-shaft,  or  weigh-shaft. 

The  end  of  the  rock-shaft  arm  is  provided  with  a  block  operated  by  a  screw  so  that  the  valve  may 
be  adjusted  without  moving  the  weigh-shaft.  The  line  of  motion  of  this  block  is  so  designed  that 
when  the  link  is  in  position  for  full-gear  forward  the  movement  of  the  block  will  be  in  line  with  the 
bridle-bars,  and  any  adjusting  motion  communicated  without  loss. 


98 


VALVES,   VALVE -GEARS  AND  VALVE  DIAGRAMS 


The  eccentric-rod  P  (Fig.  127),  by  means  of  forked  ends,  is  connected  to  the  pins  A  and  B,  Fig. 
126,  and  similarly  Q  is  connected  at  C  and  D.  G  is  the  link-block  through  which  the  link  slides, 
and  to  which  the  valve-stem  is  directly  attached;  and  E  and  F,  the  pins  to  which  the  bridle-rods  are 
connected.  The  pins  E  and  F  are  independent  of  the  link-block,  and  may  be  placed  at  the  center  as 
shown,  or  at  the  ends  as  extensions  of  H  I,  or  J  K,  or  at  intermediate  positions  according  to  the  re- 
quirement of  the  design. 

DRAFTING  TABLE  PROBLEM,  No.  7. — COMPARISON  OF  RESULTS  FROM  OPEN  AND  CROSSED-RODS. 

Comparison  of  Theoretical  Indicator-Cards  for  a  Standard  Locomotive  Using  Link-Motion  with  Open-Rods,'  and 

^  Cutting  off  at Stroke,  with  those  for  an  Engine  having  all  Conditions  the  same  Excepting  that 

Crossed-Rods  are  used. 

With  the  valve  and  valve-gear  data  given,  this  problem  is  most  readily  solved  by  finding  the  vir- 


m 


FIG.  128. 

tual  eccentric  which  would  give  the  same  motion  to  the  valve  as  the  link  does  for  the  specified  cut-off. 
This  may  be  done  graphically  :  as  follows : 

Lay  off  o'  p',  Fig.  128,  equal  to  the  distance  between  the  centers  of  the  eccentric-pins  on  the  link, 
using  any  convenient  scale.  With  o'  and  p'  as  centers,  and  with  a  radius  equal  to  the  length  of  the 
eccentric-rod,  describe  arcs  intersecting  at  o  and  draw  o  o'  and  o  p'.  Through  o  and  d  (the  center  of 
o'  p'}  draw  fod,  the  central  line  of  motion  of  the  valve-gear. 

With  a  radius  o  a  equal  to  the  radius  of  the  eccentric,  draw  the  eccentric  circle  ablto  any  con- 
venient scale.  Describe  the  lap  circle  o  h ;  lay  off  the  full-gear  lead  h  k;  and  draw  a  A;  6  perpendicu- 
lar to  o  d,  thus  obtaining  a  and  6,  the  positions  of  the  eccentric-centers  for  full-gear. 

a  o  i  —  the  angle  of  advance,  o  a  and  o  b  are  the  diameters  for  Zeuner  circles  for  the  link  in  full- 
gear,  for  either  open  or  crossed-rods.  With  open-rods  o  a  will  be  the  position  of  the  eccentric  radius 
for  going  forward  (i.e,  running  "under")  and  o  b  for  backing  (i.e.  running  "over"),  it  being  kept  in 
mind  that  a  reversing  rocker  is  used  and  that  the  crank  is  at  o  c. 

1  For  complete  graphical  demonstration,  see  "Designing  Valve-Gearing,"  by  E.  J.  C.  Welch,  pp.  105  to  141. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


99 


The  travel  of  the  valve,  and  the  events  of  the  stroke  are  thus  determined  by  the  Zeuner  circle  a  k  o, 
for  full-gear.  With  the  slide-block  at  any  other  position,  such  as  at  r',  the  virtual  eccentric  may  be 
found  as  follows  for  forward  running: 

Draw  a  c  perpendicular  to  o  o'',  this  perpendicular,  extended,  cuts  the  central  line  of  motion  at  c 
and  gives  h  c  as  the  mid-gear  lead.  A  circular  arc  drawn  through  the  points  acb  corresponds  closely 
with  the  curve  containing  the  loci  of  the  extremities  of  the  diameters  of  the  Zeuner  circles  (or  the 
centers  of  the  virtual  eccentrics)  for  all  intermediate  positions.  Therefore  the  virtual  eccentric  for 
the  slide-block  at  r'  has  a  radius  o  r,  found  by  making  a  r  :  a  c  b  :  :  o'  r'  :  o'  s  p',  and  the  Zeuner  circle 
n  r  o  determines  all  the  events  of  the  stroke  but  not  crank  positions.  They  will  only  be  determined 
if  the  Zeuner  circles  are  in  the  proper  quadrant.  If  the  position  of  the  slide-block  is  desired  for 
a  given  cut-off  as,  for  example,  with  the  crank  at  om,r  is  found  by  drawing  n  r  perpendicular  to  o  m 
and  tangent  to  the  lap-circle;  and  r'  by  the  proportion  just  given. 

If  the  link  is  actuated  by  crossed-rods  the  slide-block  (represented  at  r'  for  open-rods)  would  be  at 
r"  (r"  p'  =  r'  o')  to  give  the  same  cut-off  as  before,  and  the  Zeuner  circle  n  q  o  would  show  the  steam 
distribution.  The  arc  a  ebis  found  by  drawing  a  u  perpendicular  to  the  mean  eccentric  position  o  pr 
for  crossed-rods,  and  noting  the  point  e  where  the  perpendicular  crosses  the  central  line  of  motion. 

The  necessary  data  for  this  problem  may  be  taken  from  the  first  eight  items  of  the  following  table 
•  of  dimensions  of  the  valve-gear  of  a  locomotive : 

Stroke  of  piston '. 24" 

Maximum  travel  of  valve . 

Steam-lap 

Exhaust-lap 0 

Lead,  full-gear ^ 

Length  of  connecting-rod 92" 

Length  of  eccentric-rods 57J- 

Distance  apart  of  eccentric-pins 12" 

Distance  of  eccentric-pins  behind  link-arc 3" 

Distance  of  tumbling-shaft  from  main  shaft 44" 

Radius  of  tumbler 17" 

Radius  of  hanger 

Tumbling-shaft  above  main  shaft 

Height  of  rock-shaft  above  main  shaft ...... 

Mid-gear  lead  same  on  both  strokes. 

Enter  a  table  of  results  on  the  plate  as  follows : 


Per  Cent,  of  Completed  Stroke 

Lead. 

Admission 

Cut-off. 

Release. 

Compression 

open-rods  

crossed-rods  

open-rods  

crossed-rods  .  . 

NOTE:  Take  initial  boiler  pressure  of  85  Ibs.  gauge  with  2  Ibs.  back  pressure  and  a  40  spring, 
ance  volume  of  5%.     Make  the  indicator  cards  4  inches  long. 


Assume  a  clear- 


100  VALVES,   VALVE-GEARS  AND   VALVE  DIAGRAMS 

TYPES  OF  VALVE-GEARS. 
Gooch  Gear. 

The  link  for  this  valve-gear  is  a  "stationary"  one  and  is  shown  in  Fig.  129.  The  characteristics 
of  the  gear  are: 

1st.  That  with  the  engine  on  dead-center  the  slide-block  moves  up  and  down,  while  the  link 
remains  stationary. 

2d.  That  the  link  curvature  is  convex  to  the  engine-shaft,  and  has  for  the  radius  the  length  of 
the  radius-rod. 

From  the  method  of  construction  of  this  form  of  gear  it  will  be  observed  that  the  slide-block 
may  be  moved  from  one  end  of  the  link  to  the  other  without  altering  the  position  of  the  valve. 
This  means  that  the  lead  opening  (shown  in  the  sketch  of  the  valve  section,  Fig.  129),  is  constant 
for  all  positions  of  the  slide-block  in  the  link.  With  the  Stephenson  link  the  lead  opening  is  depend- 


FIG.  129.— Gooch  Gear. 

ent  on  the  arrangement  of  the  eccentric-rods,  but  with  the  Gooch  link  the  result  remains  the  same 
whether  open  or  crossed-rods  are  used. 

The  Gooch  gear  takes  much  more  space  than  the  Stephenson  gear  on  account  of  the  radius- 
rod. 

For  stationary  engines  the  Gooch  gear  is  especially  adapted  for  use  in  connection  with  a  gov- 
ernor, for  the  reason  that  the  radius-rod  throws  a  much  less,  and  more  easily  balanced  load  on  the 
governor  than  does  the  shifting  link  with  its  rods,  hanger,  additional  friction,  etc. 

Allen  Gear. 

The  special  features  of  this  form  of  gear  are  the  straight-line  link  k  n,  and  the  simultaneous 
operation  of  the  link  and  the  radius-rod  (k  I)  through  the  suspension-rods  /  g  and  d  h  pivoted  to 
the  rocker-arms  e  f  and  e  d,  Fig.  130. 

The  main  object  in  laying  out  a  design  using  the  Allen  link  is  to  so  proportion  the  lengths 
of  these  reversing-arms  that,  as  the  link  moves  up  and  the  radius-rod  down,  the  point  k  will  move 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


101 


to  /e,  in  as  nearly  an  arc  about  I  as  possible.  If  it  moved  in  a  circular  arc  the  valve  would  have  a 
constant-lead  opening,  as  in  the  Gooch  motion.  The  Allen  link  gives  less  variable  lead  than  the 
Stephenson,  and  with  long  eccentrics  and  radius-rod  the  lead  is  practically  constant.  Properly 


FIG.  130.— Allen  Gear. 

designed  reversing-arms  tend,  incidentally,  to  equalize  the  moments  on  the  two  sides  of  the  revers- 
ing-shaft  e.    The  sketch  is  somewhat  distorted  to  avoid  overlapping  of  lines;  b  k,  should  equal 


Fia.  131— Fink  Gear. 


b  k,  and  a  n'  should  equal  a  n.    Directions  for  proportioning  these  arms  may  be  found  in  "Link  and 
Valve  Motions,"  by  Auchincloss,  pages  140  to  142. 

Fink  Gear. 

Fig.  131  shows  a  center-line  diagram  of  the  Fink  gear.     The  point  o  is  the  engine-shaft,  o  a 
the  eccentric-arm,  and  o  b  the  crank  in  line  with  o  a.    The  eccentric-rod  a  d  is  rigidly  connected  at 


102 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


d  to  the  link-arc  e  f.  The  radius-rod  e  j  connects  at  j  with  the  valve-stem.  The  arc  e  f  is  drawn 
with  e  j  as  a  radius  so  as  to  maintain  a  constant  lead  at  all  gears.  The  point  g  in  the  eccentric- 
rod  is  designed  to  move  in  an  arc  coinciding  as  nearly  as  possible  in  the  line  o  j  by  being  pivoted 
to  the  radial  arm  g  h  as  shown.  This  mechanism  causes  the  link-arc  to  move  up  and  down  and  thus 
give  motion  to  the  slide-block  e,  which  moves  back  and  forth  and  across  the  upper  half  of  the  arc  of 
each  cycle  when  running  full-gear  forward,  and  across  the  lower  half  when  running  full-gear  back- 
ward. The  travel  of  e,  and  consequently  the  travel  and  cut-off  of  the  valve,  is  regulated  by  the 


FIG.  132.— Porter-Allen  Gear. 


suspension-rod  k  n,  operated  by  the  arm  k  I.    A  mathematical  discussion  of  this  motion  may  be 
found  on  pages  87  to  94  in  "Valve  Gears,"  by  Spangler. 

Porter- Allen  Gear. 

This  gear  is  a  modification  of  the  Fink  motion  just  described.  It  has  been  manufactured  for 
many  years  at  the  Southwark  Foundry  in  Philadelphia,  and  is  in  service  in  a  large  number  of  indus- 
trial plants  throughout  the  country. 

The  eccentric  is  represented  by  the  heavy  weight  line  a  6  in  Fig.  132,  and  the  crank  by  the 
medium  weight  line  a  r,  and  both  are  set  in  the  same  direction.  The  center  of  the  eccentric-sheave 
is  at  b  and  the  circle  6,  6,,  6a,  6S,  is  the  path  of  the  eccentric-center.  If,  in  the  Fink  gear,  the  point 
d  is  moved  back  to  coincide  with  g,  the  principle  feature  of  the  Porter-Allen  motion  is  obtained. 
The  latter  gear  is  usually  made  to  give  variable  cut-off  only  and  therefore  the  reversing  arc  (repre- 
sented by  df  in  the  Fink  motion)  is  omitted  in  Fig.  132.  The  Porter-Allen  gear  operates  separate 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


103 


live  steam  and  exhaust  valves,  the  latter  through  the  rod  p  q,  which  it  will  be  observed  is  not  adjust- 
able and  therefore  gives  constant  release  and  compression  for  all  cut-offs. 

The  path  of  the  point  e  of  the  eccentric-strap  arm  is  represented  by  the  closed  curve,  e,  e1}  e^,  e3, 
while  the  path  of  the  point  e  of  the  rod  e  g  is  represented  by  a  curved  line  not  shown  in  the  sketch, 
but  which  the  student  should  be  prepared  to  draw.  Since  these  two  paths  do  not  coincide,  there 
will  be  continuous  slipping,  or  a  quivering  action,  between  the  slide-block  pin  and  the  guide-arc 
at  e,  such  as  is  common  to  curved  link-motions  generally.  The  arc  e  c  has  g  for  its  center  and 
therefore  constant  lead  is  obtained  at  all  cut-offs.  The  manner  in  which  the  governor  controls 
the  cut-off  is  shown  in  the  sketch. 

Walschaert  Gear. 

The  mechanism  composing  the  Walschaert  valve-gear  is  entirely  different  from  any  thus  far  con- 
sidered. The  resultant  motion  of  the  valve  is  due  to  two  independent  component  motions,  one  pro- 
duced by  the  eccentric-pin,  c,  the  other  by  the  crosshead,  as  shown  in  Fig.  133. 

a  is  the  center  of  the  engine-shaft,  and  a  b  the  main  crank.  The  eccentricity,  a  c,  is  obtained 
by  keying  the  eccentric  crank  b  c  to  the  main  crank-pin,  b,  outside  of  the  connecting-rod,  a  c  is 
taken  'at  right  angles  to  a  b,  and  the  angle  of  advance,  therefore,  is  zero:  this  means,  of  course, 
that  so  far  as  the  eccentric  motion  is  concerned  the  valve  could  have  neither  lap  nor  lead  and  steam 
would  be  admitted  for  full  stroke,  as  explained  on  page  2  of  these  notes.  The  link  r  s  oscillates  on 
a  fixed  shaft  shown  at  k  in  Fig.  133  and  at  Wi  in  Fig.  134.  Any  desired  valve-travel  and  cut-off 
for  either  forward  or  backward  motion  of  the  valve  may  be  obtained  by  shifting  the  slide-block 
k  (attached  to  the  radius-rod)  along  the  link  r  s,  by  means  of  the  radius-rod  hanger. 

The  arm  d  e,  which  is  firmly  fixed  to  the  crosshead  at  one  end,  connects  at  the  other  by  means 
of  a  connecting  link  with  the  lap  and  lead  lever  /  g  h.     This  lever  so  combines  the  component  eccen- 
tric and  crosshead  motions  that  the  latter  makes  up 
for  the  angular  advance  which  was  neglected  in  laying 
out  the  eccentric-center  c. 

A  general  analysis  of  this  motion  may  be  carried 
out  by  dividing  the  eccentric  and  crank  circles  into  an 
equal  number  of  parts,  starting  at  c  and  b  and  finding, 
by  construction,  the  corresponding  positions  of  the  lap 
and  lead  lever,  as  shown  in  Fig.  135. 

In  laying  out  and  adjusting  the  Walschaert  gear  it 
should  be  noted: 

1.  That  in  order  to  get  constant  lead  for  all  run- 
ning positions,  the  link-arc  r  s  must  have  a  radius  equal 
to  the  length  of  the  radius-rod  g  k  and  that  when  the 
main  crank  is  on  either  dead-center  the  connections 
through  the  eccentric-crank,  eccentric-rod  and  link 
must  be  such  that  the  link-arc  r  s  has  the  correspond- 
ing position  g  of  Fig.  133  as  a  center.  Then,  no  matter 
where  the  link-block  k  may  be  located,  whether  at  the 
FlG  13;T  extremes  for  full-gear  (fc,  Fig.  134),  or  the  center  for  mid- 

gear  (k,  Fig.  133),  the  lead  will  be  the 'same,  for  A;  may 
be  moved  along  the  link,  when  in  the  position  just  described,  without  moving  the  valve. 

2.     The  lap  and  lead  lever  should  be  vertical  when  the  piston  is  at  the  middle  of  the  stroke  and 


104 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


the  radius-rod  in  the  mid-gear  position;  also  its  length  should  be  chosen  so  that  its  angular  vibration 
shall  not  exceed  60  degrees,  preferably  45  to  50°. 

3.    The  rod  e  f  should  vibrate  through  equal  angles  above  and  below  a  horizontal  line. 

Radial  Valve-Gears. 

With  the  Walschaert  gear,  just  described,  and  the  Hackworth  and  Marshall  gears  about  to  be 
taken  up,  it  will  be  noticed  that  variable  travel  of  the  valve,  with  consequent  variable  cut-off,  and 
also  forward  and  backward  running,  are  obtained  with  the  use  of  only  one  eccentric  or  its  equivalent. 
The  final  motion  given  to  the  valve-stem  in  each  case  is  the  resultant  motion  of  that  due  to  the 


FKJ.  136.— Hackworth  Gear. 

eccentric,  and  to  some  other  mechanical  feature,  which  latter  distinguishes  the  name  of  the  gear. 
In  addition  to  the  gears  just  mentioned  there  are  other  types  too  numerous  to  describe  here;  all  of 
this  style  are  frequently  grouped  under  the  head  of  radial  valve-gears,  the  characteristic  feature  being 
that  the  resultant  motion  of  the  valve  is  taken  from  a  vibrating-link.  In  the  case  of  the  Joy  gear 
soon  to  be  described  there  is  not  even  one  eccentric,  but  nevertheless  the  vibrating-link  is  obtained. 
The  general  advantages  of  radial  valve-gears  are:  Lightness,  compactness,  small  number 
of  moving  parts,  and  constant  lead.  The  general  disadvantages  are:  Unequal  valve  motion,  un- 
less vibrating-lever  is  long  (Hackworth  gear  excepted),  large  transverse  stress  on  vibrating-link  in 
case  of  an  unbalanced  valve,  or  of  high  speed. 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


105 


Hackworth  Gear. 

In  Fig.  136  o  a  is  the  engine-crank,  and  o  b  the  eccentric  which,  in  this  gear,  is  always  set  either 
with  the  crank,  or  180°  from  it.  6  d  is  the  vibrating-link  and  is  of  constant  length;  ef  a  slide-bar 
pivoted  at  the  point  g;  k  I  the  valve-stem  and  k  c  the  valve-stem  connecting-rod,  c  m  n  is  the  path 


R&ach  rod  - 
w  to  rwersmg  lever 


FIG.  134.— Walschaert  Gear. 


of  the  point  c.     The  fixed  point,  d,  on  the  vibrating-link  travels  forward  and  back  on  the  slide-bar 
once  during  each  revolution. 

By  adjusting  the  inclination  of  the  slide-bar,  the  resultant  vertical  motion  of  the  valve  is  modified, 
and  the  point  of  cut-off  varied.    When  the  slide-bar  is  horizontal  the  valve  motion  is  a  minimum; 


106  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

when  its  inclination  is  reversed,  as  shown  at  h  i,  the  engine  is  reversed,  o  p  is  the  outward  dead- 
center  position  of  the  crank.  When  the  crank  is  on  dead-center  the  vibrating-link  is  at  q  g,  or  r  g, 
and  the  valve  is  off  center  a  distance  s  t  or  t  u.  These  distances  are  the  same,  and  are  equal  to  the 
lap  plus  the  lead.  Therefore  if  the  lap  is  the  same  on  both  ends  of  the  valve,  the  lead  is  the  same  and 
is  constant  for  all  running  positions,  and  is  independent  of  the  inclination  of  /  e.  According  to  the 
requirements  of  the  design  the  eccentric,  which  must  be  in  line  with  the  crank,  may  be  either  on  the 
opposite  side  or  on  the  same  side;  and  the  valve  motion  may  be  taken  from  the  vibrating-link  on 
either  side  of  the  slide-bar,  at  c  or  at  v.  These  selections  depend  chiefly  upon  whether  the  valve  ad- 
mits steam  from  the  inside  or  outside. 

This  valve-gear  gives  a  good  steam  distribution,  and  is  compact.  The  objection  to  it  lies  in  the 
excessive  friction  between  the  slide-bar  and  slide-block.  The  slide-block  in  some  designs  is  provided 
with  rollers. 

Marshall  Gear. 

This  gear,  shown  in  Fig.  137,  is  largely  used.  It  is  a  modification  of  the  Hackworth  gear  in 
which  the  straight  slide-block  is  replaced  by  a  swinging  pin  moving  in  a  circular  arc.  o  a  represents 
the  crank,  o  b  the  eccentric,  b  d  the  vibrating-link,  k  c  the  valve-stem  connecting-rod,  and  I  k  the 
valve-stem.  The  point  d  of  the  vibrating-link  swings  in  the  circular  arc  /  h  about  e  as  a  center. 
The  pivot  e  is  at  the  end  of  the  arm  g  e,  which  is  keyed  to  a  reversing  shaft  at  g.  The  position  of 
the  arm  g  e  is  shown  in  solid  lines  for  full-gear  forward.  This  position  of  the  arm  gives  the  maxi- 
mum travel  to  the  point  c,  from  which  the  valve  motion  is  taken.  This  travel  is  represented  by 
the  dotted  curve  c  m. 

When  the  arm  g  e  is  perpendicular  to  o  g  the  motion  of  d  is  approximately  on  the  line  o  g,  and  the 
motion  of  c  is  a  minimum,  as  represented  by  the  dotted  closed  curve  c'  m'.  To  reverse  the  engine  for 
full  speed  backward  the  arm  g  e  is  thrown  to  g  e4. 

With  the  pivot  at  e  the  cut-off  is  maximum ;  at  e,  it  is  earlier,  and  at  e^  it  is  minimum  and  the  port- 
opening  is  equal  to  the  lead. 

In  the  Marshall  gear  the  eccentric  is  always  in  line  with  the  crank,  either  on  the  same  or  opposite 
sides  of  the  shaft,  as  in  the  Hackworth  gear.  The  constant  quantity,  lap  +  lead,  for  all  cut-off 
positions  is  shown  at  s  t  and  t  u  in  Fig.  137,  the  same  as  in  Fig.  136.  Also  the  valve  motion  may  be 
taken  from  x  as  well  as  from  c  should  the  design  require  it.  In  the  Marshall  gear  the  valve-travel  on 
the  head  and  crank  ends  is  not  symmetrical,  as  may  be  seen  by  the  different  lengths  y  and  z  of  the 
maximum  ordinates  of  the  curve  c  m  on  the  opposite  sides  of  o  0,  due  to  the  point  d  moving  in  an  arc 
of  a  circle.  Should  this  irregularity  affect  the  design  to  any  appreciable  extent  it  may  be  remedied 
by  introducing  a  rocker. 

Some  general  proportions  for  the  Marshall  gear  are  given  by  Mr.  Braemme,  after  whom  this  gear 
is  sometimes  called  (" Braemme-Marshall  radial  valve-gear")  as  follows: 

Length  of  supporting  arm  g  e  and  suspension-rod  de =6X0  b. 

Eccentric-rod  6  d  (exaggerated  in  Fig.  137) =6X06. 

Lead  arm  dc =  4.5  X  o  6. 

Angle  a  should  not  be  more  than  25° 

In  connection  with  the  Hackworth  and  Marshall  gears  the  student  will  be  required  to  assume 
the  data  given  in  the  first  two  columns  of  accompanying  table  and  to  fill  out  columns  3  and  4  and 
draw  a  center-line  sketch  of  either  gear  to  illustrate  the  work. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


107 


Angle  between   crank 
and  eccentric. 


0° 

0° 

180C 

180° 


Location  of  c 


Kind  of  valve  admission. 
Inside  or  outside. 


Left  of  d 
Right  of  d 
Left  of  d 
Right  of  d 


Direction  of  rotation  of 
engine  with  d  moving 
from  upper  left  to  lower 
right. 


FIG.  137.— Marshall.  Gear. 

Joy  Valve-Gear. 

This  gear,  sometimes  called  a  " compound  radial  gear,"  does  away  with  the  eccentric  altogether, 
the  valve  motion  being  obtained  solely  from  the  connecting-rod  by  a  series  of  rods  or  arms. 

o  a,  Fig.  138,  represents  the  crank,  a  6  the  connecting-rod,  c  e  and  d  k  vibrating-rods,  e  f  an  arm 
of  which  the  point  e  moves  always  in  arc  about/  as  a  center,  ij  (a  guide-arc  for  h)  is  pivoted  at  g, 
and  constructed  so  that  it  may  be  temporarily  fixed  in  any  position,  as,  for  example,  that  shown 
by  the  dotted  position,  t,  j,.  The  position  of  this  guide-arc  determines  the  point  of  cut-off.  The 
dotted  ovalsjthrough  c  and  d  show  respectively  the  paths  of  these  points,  no  matter  what  the  cut-off 


108 


VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 


gear.  The  oval  through  k  shows  the  path  of  k  for  the  position  i  j  of  the  guide-arc.  This  oval 
varies  for  different  cut-offs,  and  in  the  mid-gear  position  the  tangent  to  i  j  at  g  would  be  a  vertical 
line,  thus  giving  a  minimum  travel  to  k  and  to  the  valve,  which  should  equal  lap  plus  lead. 

When  the  engine  is  on  dead-center  d  is  at  dl}  h  at  g,  and  k  at  k  ,  and  the  horizontal  distance 
from  kl  to  the  vertical  center-line  shows  the  amount  the  valve  is  off  center,  which  in  the  dead- 
center  position  equals  lap  plus  lead.  The  engine  is  reversed  with  this  gear  by  swinging  the  guide- 


,  -  Ha/fva/w  fare/ 

i 

.-Lap  tie  ad 


f 


FIG.  138.— Joy  Gear. 

arc  about  g  beyond  the  mid-gear  position  to  it  jz.     In  the  dead-center  position  the  line  through  p 
and  g  should  be  perpendicular  to  o  b. 

The  effect  of  the  angularity  of  the  rod  k  c  in  the  Marshall  gear  (Fig.  137)  is  partially  neutralized 
with  the  Joy  gear  by  the  vibrating-rod  e  c.  When  properly  proportioned  the  Joy  gear  gives  a  rapid 
motion  to  the  valve  when  closing  the  ports,  less  compression  at  short  cut-off  than  a  Stephenson 
link  motion,  and  a  nearly  equalized  cut-off  for  all  grades  of  the  gear.  It  gives  a  constant  lead. 
These  points,  favorable  to  the  Joy  gear,  are  counterbalanced  in  part  by  the  number  of  parts  and 
joints  that  are  liable  to  give  trouble  with  wear,  and  the  obstruction  it  offers  to  proper  care  and 
attention. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


109 


It  will  be  noticed  that  the  Joy  valve-gear  is  practically  the  same  in  construction  and  principle 
as  the  Hackworth  and  Marshall  gears  from  the  point  d  to  I.  The  path  of  d  in  the  Joy  gear  takes 
the  place  of  the  eccentric  in  the  other  two. 

Baker  Gear. 

This  gear  has  been  very  recently  developed  in  connection  with  American  locomotive  construc- 
tion. It  not  only  does  away  with  the  eccentric  but  also  with  the  curved  link,  and  there  is  no  slid- 
ing friction  whatever  in  the  gear.  Illustrated  in  Fig.  139,  it  will  be  seen  that  the  part  of  the  mechan- 
ism from  a  to  j  contains  the  crosshead  and  return-crank  drive  characteristics  of  the  Walschaert 
gear,  while  the  remaining  parts  are  suggestive  of  the  Marshall  gear. 

The  Baker  gear  is  a  modification  of  the  Baker-Pilliod  gear  which  came  into  use  in  1908,  but  its 


FIG.  139.— Baker  Gear. 


manufacture  was  discontinued  two  years  later  in  favor  of  the  Baker  gear,  notwithstanding  the  fact 
that  forty-three  railroads  had  installed  the  original  gear  during  that  period. 

The  names  of  the  gear  parts  are:  Crosshead  arm,  a  6,  Fig.  139;  union  link,  6  d;  combination 
lever  d  e  f  (all  one  piece) ;  bell-crank,  e  t  s  (the  arm  e  f  on  the  combination  lever  falls  behind  the 
arm  e  t  of  the  bell-crank  for  the  phase  shown  in  the  illustration) ;  gear-connection  rod,  s  k  j  (one 
piece) ;  radius-bar,  k  I;  reverse  yoke,  m  I  n;  reach-rod,  p  n;  reverse  arm  o  p  q;  reach-rod,  q  r;  reverse 
lever,  r  u;  crank,  g  h;  return-crank,  h  i;  eccentric-rod,  i  j;  connecting-rod,  h  a. 

The  mechanism  is  shown  in  position  for  full-gear  forward.  In  order  to  follow  more  closely  the 
motion  of  the  various  parts  during  one  cycle,  the  cycle  has  been  marked  at  six  phases  and  the  paths 
and  directions  of  the  several  points  drawn.  All  fixed  centers  are  indicated  by  vertical  and  hori- 
zontal center  lines. 

When  running  forward  the  reverse  yoke  m  n  remains  stationary.  To  give  earlier  cut-off  m  n 
is  thrown  over  toward  m  nu;  and  to  run  backward  it  is  thrown  beyond  nu  until  full-gear  back- 
ward is  reached  at  m  nR. 

The  pivot,  i,  it  will  be  noted,  is  fixed  90°  behind  the  crank  and  therefore  has  zero  angle  of 
advance,  and  the  motion  from  it  alone  would  call  for  an  elementary  valve  without  lap,  and  would 
admit  steam  for  full  stroke.  The  motion  from  the  crosshead  gives  the  additional  travel  to  the 


110  VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 

valve  necessary  to  make  up  for  lap  and  lead,  and  in  this  general  respect  the  Baker  and  Walschaert 
gears  are  the  same,  although  the  actual  valve  motions  at  the  succeeding  phases  of  the  travel  are 
different  in  the  two  gears,  thus  permitting  different  claims  to  be  made  for  the  respective  gears. 
These  claims  may  be  followed  and  analyzed  from  actual  measurements  of  the  gears,  or  from  work- 
ing drawings,  by  following  the  paths  of  the  various  points  in  a  manner  similar  to  that  shown  in 
Fig.  139  when  drawn  to  a  greatly  enlarged  scale. 

When  the  mechanism  is  set  at  mid-gear,  with  m  n  at  m  nM,  the  arc  of  swing,  k  /c4,  will  have  Ijf 
for  its  center  and  s  will  remain  stationary  at  s2.  With  s2  stationary,  e  will  also  remain  at  rest  at  ea 
and  the  eccentric  will  impart  no  motion  to  the  valve.  Under  these  conditions  the  only  motion 
the  valve  has  comes  from  the  crosshead,  the  gear  being  so  proportioned  that  the  half  valve-travel 
is  then  equal  to  lap  plus  lead.  As  the  reverse  gear  is  thrown  from  the  mid-gear  position  either 
forward  or  backward  the  port  opening  increases  but  the  lead  remains  constant,  the  gear  thus  giving 
results  quite  similar  to  those  produced  by  the  straight-slot  eccentric  with  constant  lead  and  variable 
preadmission. 

The  illustration  shows  an  outside  admission  gear.  If  a  valve  with  inside  admission  is  used  the 
bell-crank  is  placed  ahead  of  the  reverse  yoke,  and  the  point  /  below  e.  The  eccentric  follows  the 
main  crank  for  both  inside  and  outside  admission. 

Stevens  Gear. 

The  Stevens  valve-gear  was  invented  by  Mr.  Francis  B.  Stevens,  E.  D.,  in  the  year  1839,  and 
is  now  used  on  nearly  all  of  the  side-wheel  excursion  craft,  and  on  most  of  the  side-wheel  ferry- 
boats. It  is  illustrated  in  Fig.  140. 

In  this  gear,  steam  is  admitted  to  the  cylinder  through  a  double-seat  poppet-valve.  There  are 
two  double-seat  valves  at  the  top  of  the  cylinder,  one  for  the  entering  steam  and  one  for  the  exhaust 
steam.  There  are  also  two  similar  valves  at  the  bottom  of  the  cylinder,  usually  below  the  floor 
line.  An  eccentric  attached  to  the  paddle-wheel  shaft  transmits  its  motion,  through  the  trussed 
eccentric-rod  and  the  rock-shaft  crank,  to  the  rock-shaft  to  which  are  rigidly  attached  cams,  or 
wipers,  as  they  are  usually  called.  These  wipers  work  against  toes,  which  are  rigidly  attached  to 
the  steam  and  exhaust-rods.  These,  through  the  valve-lifter,  raise  and  lower  the  double-seat 
valves. 

On  the  large  excursion  steamers  one  eccentric  only  is  generally  used  for  the  live  steam  and  one 
for  the  exhaust.  On  ferryboats  there  are  two  live-steam  eccentrics,  one  for  going  forward  and 
one  for  going  backward,  and  also  two  eccentrics  operating  the  exhaust.  Where  only  one  eccen- 
trcis  used  for  live  steam  the  valve  must  be  operated  by  hand  while  the  engine  is  backing. 

In  order  to  start  an  engine  having  this  gear,  it  is  necessary  for  the  engineer  to  operate  the  valve 
through  his  own  effort.  This  is  accomplished  through  the  starting-bar  lever  and  the  auxiliary,  or 
starting  rock-shaft,  to  which  are  attached  a  duplicate  set  of  wipers,  in  miniature,  operating  on 
auxiliary  toes  on  the  steam-rods.  The  effort  required  for  this  work  is  not  excessive,  as  the  double- 
seat  valve  is  practically  a  balanced  valve.  A  slight  inequality  of  balance  results  from  the  fact  that 
the  disc  A  must  be  smaller  in  diameter  than  the  disc  B  so  as  t.o  pass  through  the  valve-seat  at  B  when 
the  engine  is  being  set  up.  In  addition,  weights  are  adjusted  to  the  starting  rock-shaft  to  counter- 
balance the  weight  of  the  moving  parts. 

In  practice  the  weight  of  the  valves,  rods,  lifters,  etc.,  is  sufficient  to  cause  the  valves  to  seat 
quickly  and  firmly  enough  to  give  a  sharp  cut-off.  In  order  to  aid  the  sharpness  of  the  cut-off,  how- 
ever, some  builders  place  sjmngs  on  the  live-steam  rods. 


Plan 


Walking- 
b  e.ei  m. 


Pi  st  on  -rod 

a  Ive  //  ffers 
U pa  e  r   ex  ha ust- 
sream    valve-rod. 


Valve-lifter. 


Steam 
valve- 
red.  ' 


L/jyjoer  dcu 

'live- steam  va/ve 


Throttle 
hand/e.. 


Guietc  - 

Unheoki 
h  an  die 


Padd/e-whtel 
shaft. 


BacA 
exhaus 
ccen.pin 


Lower 
exhaust 
rod. 


Front    e  legation. 


Side    elevation. 


FIG.  140. — Stevens  Gear. 


112 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


In  this  gear  the  cut-off  position  remains  constant,  and  variation  of  speed  is  attained  by  throttling. 
The  engine  is  reversed  by  the  engineer  through  the  starting-bar  by  means  of  which  he  can  open  the 
top  or  bottom  steam-valves  and  corresponding  exhaust-valves  at  pleasure. 

In  the  front  elevation,  Fig.  140,  the  columns  and  hand-wheels  at  C  D  represent  the  connection 
leading  to  the  valve  in  the  water-pipe  supplying  the  jet  condenser. 

The  diagrammatic  sketch,  Fig.  141,  may  help  in  picking  out  from  the  detail  of  lines  in  Fig.  140, 
the  essential  kinematic  action  of  the  valve-gear.  The  piston  is  indicated  by  the  dash  line  at  k  at  the 


T^1 

<i 

7 

L  

-  —  — 

r~  — 

K 

J 

I 

n, 


FIG.  141. — Diagram  of  Stevens  Gear. 

top  of  the  stroke.  The  paddle-wheel  shaft  is  at  a  and  the  crank  at  a  b.  For  running  ahead,  as 
shown  by  the  arrow  marked  "ahead,"  the  piston  must  start  to  move  down,  the  valve  j  must  be 
moving  up  and  be  up  a  distance  equal  to  the  lead  for  the  phase  illustrated.  In  order  that  these  mo- 
tions may  occur,  using  the  toe  and  wiper' cams,  as  shown  at  g  and/,  it  will  be  evident  that  the  eccen- 
tric center  must  be  at  c  and  the  eccentric  must  precede  the  crank  a  6  by  the  angle  cab.  When  c  has 
moved  to  s,  e  is  at  r,  and  the  valve  j  is  at  its  highest  point.  Assuming  that  the  valve  just  opens 
when  the  eccentric  is  at  t,  the  angle  t  a  c  being  the  angle  of  lead,  the  total  period  of  admission  is 
represented  by  twice  the  angle  t  as.  For  running  astern,  with  the  engine  at  the  same  phase  as 
before,  the  eccentric  would  have  to  be  at  d  and  follow  the  crank  by  the  angle  dab. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


113 


Lentz  Gear. 

The  Lentz  engine  is  of  recent  date  and  also  makes  use  of  the  double-seat  poppet-valve,  the  steam 
regulation  being  accomplished,  however,  by  varying  the  cut-off  through  a  novel  type  of  shaft-gov- 
ernor and  straight-slot  eccentric  instead  of  by  throttling.  The  first  Lentz  engine  was  built  in  Ger- 
many in  1899  and  since  then  four  millions  of  horse-power  of  this  engine  have  been  built  and  installed 
in  that  country.  In  1909  the  Erie  City  Iron  Works  of  Erie,  Pa.,  obtained  the  rights  for  this  engine 
and  have  since  built  and  installed  over  50,000  horse-power  in  this  country. 

Detail  views  of  this  engine  are  shown  in  Figs.  142-145.  The  cylinder  has  four  double-seat  pop- 
pet-valves, one  at  each  corner;  the  live-steam  valve  for  the  crank  end  is  shown  in  longitudinal  section 


Lentz  Gear. 


Fig.  143 


in  Fig.  143.  The  steam  chest  is  shown  at  s  and  the  valve  at  v.  The  valve-stem  has  no  packing  but 
is  kept  tight  by  the  series  of  turned  rings,  called  water-rings,  shown  at  t.  Likewise  the  main  stuffing- 
box  at  u  is  kept  tight  by  a  series  of  iron  rings  accurately  fitted,  no  packing  being  used. 

A  transverse  section  of  the  valve-actuating  mechanism  is  shown  in  Fig.  142,  the  valve-stem  being 
actuated  by  an  oscillating  cam  shown  at  p,  acting  on  a  roller  attached  to  the  valve-stem.  The  cam 
curve  is  so  designed  as  to  disengage  from  the  roller  when  the  valve  comes  to  a  seat,  but  remains  in 
contact  until  the  valve  is  seated,  thus  preventing  noise  and  permitting  any  engine  speed.  The 
cam  surface  is  on  an  arm  of  a  bell-crank  pan,  the  other  arm  being  actuated  by  the  eccentric-rod  a  n. 
The  eccentric-center  is  at  6  and  the  eccentric  or  lay  shaft-center  at  a.  The  eccentric  shaft,  a,  runs 
longitudinally  along  the  outside  of  the  cylinder  and  gears  with  the  main  shaft  through  a  special 
form  of  bevel  gear.  The  slide-block,  y,  is  permanently  keyed  to  the  eccentric-shaft,  and  the  total 
throw  of  the  eccentric  is  twice  a  b  for  the  position  shown.  When  the  engine  speeds  up  the  governor 


114  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

throws  the  small  slide-block,  e,  which  works  in  a  small  transverse  slot  in  the  straight-slot  eccentric- 
sheave,  thus  moving  the  sheave  itself  along  the  block,  y,  and  changing  the  total  throw  of  the  eccen- 
tric to  a  minimum  of  a  z. 

The  action  of  the  governor  itself  is  unique,  and  is  illustrated  in  Figs.  144  and  145.  A  one-piece 
carrier  having  three  arms,  a  g,  af  and  a  d,  is  keyed  to  the  eccentric-shaft.  A  heavy  inertia  ring,  r, 
mounted  on  a  hollow  shaft,  m,  w^hich  turns  freely  on  the  eccentric-shaft,  gets  its  rotary  motion 
through  a  flat  circular  spring,  c  d.  Attached  to  the  hollow  shaft,  m,  is  an  arm  carrying  the  pin  e. 
As  the  engine  changes  load  and  consequently  speed,  the  inertia  ring  acts  instantly,  and  the  centrif- 
ugal weights  follow  as  soon  as  the  frictional  resistance  of  the  moving  parts  is  overcome,  to  move  the 
pin  e  and  the  eccentric-sheave  along  the  block  y.  The  governor- weights,  w,  w,  swing  on  pivots,  /,  g, 
i  nd,  through  the  links  ij  and  h  k  are  directly  connected  to  the  inertia  ring. 

Floating  or  Self -Centering  Valve-Gears. 

In  this  type  of  gear,  a  valve  with  very  small  steam-lap  is  moved  off  center  by  hand,  thus  start- 
ing an  auxiliary  engine,  the  moving  parts  of  which  automatically  return  the  valve  to  its  central 
position,  thus  shutting  off  steam  and  bringing  the  piston  to  rest  at  any  desired  position  in  its  stroke, 
depending  on  the  amount  of  motion  given  to  the  valve  at  the  start.  As  illustrated  in  Fig.  146  it 
is  used  to  operate  the  Stephenson  link  in  a  heavy  marine  engine.  The  diagrammatic  sketch  of 
Fig.  146  is  shown  in  a  general  drawing  in  Fig.  147  where  the  self-centering  gear  and  engine  are  shown 
attached  to  the  framework  of  a  large  ferryboat  engine.  To  follow  the  detail  construction  from  the 
rock-shaft,  0,  to  the  link,  refer  to  Fig.  127  in  which  0  is  the  rock-shaft. 

In  addition  to  using  these  gears,  as  above  described,  for  changing  the  cut-off,  and  for  reversing 
in  engines  which  are  too  large  to  be  operated  by  hand,  they  are  used  in  steam  hammers.  The  same 
principle  is  applied,  although  the  construction  is  different,  in  steering  engines  and  certain  types  of 
elevator  engines  where  it  is  desired  that  a  self-centering  engine  shall  turn  a  fraction  of  a  revolution 
or  a  certain  number  of  revolutions,  and  then  automatically  come  to  rest.  This  case  is  illustrated  in 
Fig.  148.  It  is  also  applied  to  steam  turbines,  as  will  be  explained  later. 

The  method  of  operating  the  gear  when  it  is  desired  to  move  the  piston  through  only  a  part  of  its 
stroke  is  as  follows :  Suppose  it  is  desired  to  move  the  Stephenson  link,  Fig.  146,  from  its  mid-gear 
or  neutral  position,  r  s,  to  its  full  speed  forward  position,  r.  Si.  This  would  be  accomplished  by  mov- 
ing the  hand  lever  a  c  b,  thus  giving  practically  simultaneous  motions  to  all  points  in  the  mechanism, 
but  in  order  to  more  sharply  define  the  explanation  it  will  be  assumed  that  the  action  of  the  mechan- 
ism takes  place  in  quick  successive  steps  as  follows: 

1.  The  engineer  moves  the  lever  from  a  to  a1}  carrying  b  to  61,  d  to  di,  e  to  d,  and  the  valve  from 
v  to  t'i,  thus  opening  the  port /to  steam  by  the  amount  e  d  less  lap.     e  e^  equals  steam-port 
width  plus  lap.     The  point  n  is  assumed  to  remain  stationary  for  the  time  being.    As  soon  as  the 
engineer  brings  the  hand  lever  in  the  position  ai  bi,  he  clamps  it  there,  thus  securing  the  end  of  the 
short  connecting  link  b  d  at  di  to  act  an  instant  later  as  a  temporarily  fixed  turning  point  for  the 
"floating"  lever  n  e. 

2.  As  soon  as  the  port/  is  opened  the  piston  moves  to  the  right,  driving  the  crosshead  from  k  to 
&,,  the  rock-shaft  lever  from  o  I  to  o  h  and  thus  securing  the  desired  rotation  of  the  rock-shaft  and  with 
it  the  required  motion  of  the  link  r  s  through  the  arm  o  p  and  the  bridle-rod  p  q.     The  "return-arm, " 
o  p,  may  or  may  not  be  in  line  with  o  I  according  to  the  construction  of  the  engine  and  framewoik. 

3.  The  point  m  of  the  rod  mnis  attached  to  the  lever  o  I  and  is  carried  by  it  to  rm,  thus  causing 
n  to  swing  to  n\  about  the  temporary  center  d\ ,  and  d  to  swing  back  to  e,  again  placing  the  valve  on 
center  and  shutting  off  steam  just  as  the  piston  reaches  hi. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


115 


Theoretically  there  should  be  no  steam-lap  on  the  valve,  but  this  gives  too  sensitive  an  action. 
In  practice  a  very  small  steam-lap  is  used — about  %  ".  The  exhaust-lap  is  added  for  cushioning 
and  may  be  about  K  "• 

If  it  is  desired  to  move  the  Stephenson  link  back  from  full  speed  ahead  to  say  half-speed  ahead, 
the  engineer  would  move  the  hand  lever  to  a  point  midway  between  «i  and  a  and  clamp  it  there. 
This  would  move  d,  halfway  to  d,  e  halfway  to  ez,  and  cause  the  valve  to  open  the  port  g  halfway 
approximately.  The  piston  would  then  be  driven  from  h^  toward  h,  and  would  come  to  rest  when  it 
had  caused  nlt  through  the  intervening  mechanism,  to  reach  a  position  midway  between  nl  and  n. 


•+/-Hand  Lever 

'C 


FIG.  146. — Floating  or  Self-Centering  Gear. 


The  new  positions  of  the  pivot  points  nt,  d,,  and  the  point  e  would  then  all  be  in  one  straight  line  and 
both  ports  would  be  closed  with  the  valve  on  center. 

Should  the  expansion  of  the  steam,  or  the  weight  of  the  moving  parts  carry  the  piston  beyond  the 
desired  position,  the  valve  would  also  be  carried  beyond  its  central  position,  thus  admitting  steam 
on  the  other  side  and  quickly  balancing  and  securing  the  piston  at  the  desired  point. 

When  the  crosshead,  or  some  other  portion  of  the  mechanism,  is  not  locked  at  a  given  running 
speed,  the  weight  of.the  piston,  crosshead,  connecting-rod,  etc.,  especially  if  these  parts  are  in  a 
vertical  position,  will  cause  the  entire  mechanism,  including  the  Stephenson  link,  to  move  gradually 
until  the  valve  is  drawn  to  one  side  by  the  amount  equal  to  its  lap,  when  steam  will  enter  the  port 
and  drive  the  piston  and  entire  gear  back  to  the  desired  position.  In  the  meantime  the  slight  chang- 


116  VALVES,  VALVE-GEARS  AND  VALVE  DIAGRAMS 

ing  of  position  of  the  Stephenson  link  has  been  gradually  changing  the  point  of  cut-off  so  that  the- 
speed  of  the  engine  has  gradually  increased  or  decreased  to  a  certain  point  and  then  suddenly  re- 
covered. This  action  is  technically  referred  to  as  "creeping,"  and  its  constant  recurrence  is  notice- 
able in  vessels  carrying  this  form  of  unlocked  gear. 

DRAFTING  TABLE  PROBLEM,  No.  8. 

Construct  a  floating  or  self-centering  valve-gear  from  the  following  data: 

Cylinder;  bore,  9";  stroke,  18". 

Steam-ports,  8"  X  1";  exhaust  port,  8"  X  1^". 

Valve-throw  for  }/%  stroke  of  piston   =  steam-port  width  and  lap. 

Steam-lap,  %";  exhaust-lap,  %". 

Width  of  bridge,  %";  width  of  piston,  2%". 

Clearance,  J£";  thickness  cylinder  wall,  JHj";  diameter  piston-rod,  1%". 

Length  of  piston-rod,  from  center  of  piston,  27";  connecting-rod  25";  valve-stem,  from  center  of  valve,  16^"- 

Total  angle  of  action  for  rock-shaft,  45°;  hand  lever,  60°. 

Ratio  of  lever  arms  (e  d:  d  n  of  Fig.  146)  1 :  3. 

Assume  proportions  for  bridle-rod,  Stephenson  link,  eccentric-rods,  etc. 

With  the  above  dimensions,  draw  the  engine  diagrammatically  about  as  shown  in  Fig.  146. 

Show  the  entire  mechanism  in  skeleton  construction  on  the  central  position,  and  also  in  the 
characteristic  line- work,  as  shown  in  Fig.  146,  for  full-gear  ahead  and  full-gear  astern  positions. 

Assume  that  the  gear  is  all  set  and  that  the  vessel  is  running  full-speed  astern.  Show  by  fine 
solid  lines  the  center-line  positions  of  each  piece  of  mechanism  after  the  engineer  has  changed  to 
half-speed  ahead. 

Label  the  eccentric-rods  properly  with  the  words  "ahead"  and  "astern."  For  running  ahead 
the  crank  w  x  is  assumed  to  turn  clockwise. 

The  pivot  point  e  is  generally  made  to  travel  in  a  straight  line  coinciding  with  the  valve-stem. 
The  points  d  and  n  travel  in  curvilinear  paths.  In  practice,  the  floating  lever  does  not  swing  through 
such  wide  angles  as  are  shown  in  the  drawing,  for  in  the  design,  as  stated  at  the  outset,  it  is  assumed 
that  the  action  on  the  pivot  points  d  and  n  takes  place  in  successive  steps,  whereas  in  the  actual 
mechanism  these  motions  occur  simultaneously,  o,  c  and  w  are  the  only  fixed  turning  points. 

The  swinging  arms  should  be  laid  out  to  have  the  same  obliquity  of  action  on  each  side  of  the 
center-line,  as  for  example,  I  should  rise  and  fall  equal  amounts  from  the  horizontal  center-line ; 
likewise,  m  n  and  p  q,  approximately,  as  these  two  have  no  definite  fixed  center-lines. 

The  ratio  of  1  :  3  for  e  d  ;  d  n  is  an  arbitrary  value  and  may  be  different  in  different  gears,  depend- 
ing on  the  proportions  of  the  other  parts. 

Steering  Gear. 

The  principle  of  the  self-centering  valve-gear  is  here  used  to  obtain  a  certain  rotation  of  a  drum 
carrying  the  tiller  rope,  for  a  given  swing  of  the  pilot's  wheel,  or,  in  other  words,  a  certain  number 
of  turns  of  the  auxiliary  steering-engine  for  a  given  motion  of  the  self-centering  valve.  This  is 
accomplished  as  follows : 

The  two  engines  A  and  A',  Fig.  148,  drive  the  shaft  B,  Fig.  149,  the  power  being  transmitted 
through  the  worm  C  and  wheel  D,  and  the  spur-gears  E  and  F  to  the  drum  carrying  the  rope  to  the 
rudder  arm. 

The  admission  of  steam  to  cylinders  A  and  A'  is  controlled  in  the  usual  way  by  the  hollow  piston 
valves  G  and  H  respectively.  The  floating  or  self-centering  valve  L  is  a  third  piston  valve  which 


Arrangement  of  Throttle  and 
Steam  Engineer-  Gear  for 
Engine. 

FIG.  147. 


Exhaust 
Steam 


Section  through  JY. 
FIG.  149. 


Sect/ on  ttjrough  WZ. 
FIG.  148. 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  119 

serves  simply  to  direct  the  live  steam  from  the  feed  pipe  into  the  passage  /  or  K,  thus  establishing 
inside  or  outside  admission  for  A  and  A',  and  therefore  determining  the  direction  that  B  will  have. 

Before  taking  up  the  action  of  the  mechanism  as  a  whole,  attention  is  called  to  the  fact  that  M 
is  a  worm  wheel  mounted  on  a  threaded  rod  R,  and  is  prevented  from  having  longitudinal  motion 
along  the  rod  by  contact  with  the  frame  shown  at  N  and  0.  R  is  connected  to  the  valve-stem  P  by 
a  swivel  joint  Q,  and  to  the  rod  S  (connected  with  the  pilot  wheel)  by  a  square-section  slip  joint, 
as  shown  in  view  T,  allowing  relative  motion  in  a  longitudinal  direction  only. 

Assume  that  a  certain  motion  of  the  pilot  wheel  results  in  the  turning  of  S,  and  therefore  R,  in 
the  direction  shown  by  arrow  I;  worm  M  will  remain  stationary,  and  the  thread  in  the  hub  will 
cause  R  and  L  to  move  down,  allowing  live  steam  to  fill  the  passage  J,  and  giving  inside  admission 
to  cylinders  A  and  A',  A'  being  the  starting  cylinder  in  the  phase  here  represented.  Since  the  two 
cranks  turning  the  shaft  B  are  set  90°  apart,  the  engine  will  always  be  in  a  position  to  start  in  the 
desired  direction.  B,  D  and  F  will  have  directions  shown  by  arrows.  The  exhaust  steam  from 
A  and  A'  will  go  from  the  cylinders  into  the  passage  K,  and  will  pass  through  the  hollow  center 
of  L  into  the  exhaust  pipe  U,  it  being  remembered  that  the  valve  L  was  placed  below  its  central 
position  by  the  initial  motion  given  by  the  pilot.  As  soon  as  the  engine  starts  the  worm  M  begins 
to  rotate  as  shown  and  by  means  of  the  thread  in  its  hub  draws  the  stem  P  and  the  "floating" 
valve  L  back  to  its  central  position  and  the  engine  stops  automatically. 

If  the  initial  motion  of  S  is  reversed,  the  valve  L  is  lifted,  allowing  the  live  steam  to  enter  K, 
thus  establishing  outside  admission  for  the  cylinders  A  and  A',  and  therefore  reversing  the  motion 
of  the  other  members,  the  engine  coming  to  rest  when  the  valve  L  is  automatically  dropped  to 
central  position. 

STEAM  TURBINE  GEARS. 

Steam  control  in  the  reciprocating  engine  requires  that  admission  must  take  place  during  periods 
that  are  intermittent  and  that  these  periods  must  be  definitely  timed  with  the  cycle.  In  the  steam 
turbine,  admission  is  continuous  or  in  puffs  in  extremely  rapid  succession,  the  quantity  being  varied 
by  the  governor  and  the  valve-gear  according  to  the  load  on  the  turbine.  Except  for  the  details  of 
construction  due  to  the  high  speed  and  exacting  conditions  under  which  the  turbine  is  operated,  the 
underlying  principles  or  turbine  valve-gear  construction  are  simplified  by  the  practically  continuous 
steam  admission. 

Both  in  the  Curtis  and  Westinghouse  turbines,  which  will  be  illustrated,  it  may  be  said  in  a 
general  way  that  greater  or  less  steam-opening  area,  as  required,  is  obtained  through  a  floating  or 
self-centering  valve-gear  operated  by  the  governor. 

Curtis  Steam  Turbine  Valve-Gear. 

In  the  Curtis  turbine,  illustrated  in  approximately  correct  proportion  in  Fig.  145,  and  diagram- 
matically  in  Figs.  146  and  147,  the  parts  are : 

A,  turbine  casing  H,  pilot-valve  (piston-valve  with  inside  admission) 

B,  generator  7,  piston 

C,  governor  casing  J,  piston-rod 

D,  governor  beam  K,  differential  connection-rod 

E,  governor  connection-rod  L,  differential  lever-arm 

F,  floating  lever  M,  differential  link 

G,  pilot-valve  connection- rod  TV,  rack 


120 


0,rspur-wheel 

P,  c.^m-shaft 

Q,  cams 

R,  cam-rollers 

jS,  controlling  valve-lever 

T,  controlling  valve-stem 

U,  poppet-valve  and  valve-seat 


V,  cross  transmission-shaft 
W,  first  turbine  wheel 
X,  controlling  lever-shaft 
Y,  steam-chest 

Z,  governor-weights  which  swing  on  knife-edges 
instead  of  pins. 


Oil,  under  pressure,  is  used  to  operate  the  piston,  7.    The  Curtis  turbine  has  multiple  admission 


GENERATOR 


B 


•N,0;P,Q 


FIG.  145. 


VALVES,   VALVE-GEARS  AND   VALVE  DIAGRAMS 


121 


valves,  each  having  its  own  controlling  mechanism,  Q,  R,  S,  T,  and  all  operated  by  a  single  cam- 
shaft, P.  Eight  separate  admission  valves  are  represented  in  the  top  view,  Fig.  147.  In  Fig.  145 
two  sets  of  multiple  valves  are  represented,  one  set  on  each  side  of  the  turbine,  both  connected  by 
a  cross-shaft,  and  all  operated  by  one  governor  and  one  floating  valve-gear. 

The  reason  for  using  multiple  valves  in  this  way  lies  in  the  fact  that  all  valves  that  are  open 


Fig. 


Fig.  146 


at  all  are  wide  open  with  one  exception  and  that  one  is  the  only  one  that  is  throttling  the  steam. 
The  nozzles  thus  receive  full  steam  pressure  and  work  to  best  advantage. 

In  the  operation  of  the  turbine,  steam  is  admitted  through  a  strainer  to  a  combined  emergency 
and  stop-valve,  not  shown  in  the  illustrations,  to  the  steam-chest,  Y.  "When  the  turbine  is  at  rest 


122 


VALVES,   VALVE-GEARS  AND  VALVE   DIAGRAMS 


and  the  governor-weights  "dead,"  all  the  valves  are  open  excepting  the  first  one,  which  is  just  ready 
to  close.  As  the  turbine  gains  speed  the  governor-weights,  Z  Z,  fly  out,  thus  causing  the  governor- 
beam,  D,  to  turn  down  about  the  center  c;  the  point,  /,  of  the  floating  lever  to  move  down  to  /i , 
turning  momentarily  about  d;  the  point,  e,  to  move  to  E, ;  and  finally  the  pilot-valve,  H,  to  move 
down  and  open  the  port  g.  As  the  piston,  /,  moves  up,  the  motion  is  transmitted  through  the 
links,  K,  L  and  M  to  d,  which  then  turns  momentarily  about  /i  thus  moving  e,  back  to  e,  closing 
both  ports.  The  piston,  /,  then  comes  to  rest  and  will  remain  stationary  so  long  as  the  speed 
remains  constant. 

As  the  piston,  /,  moves  up,  one  admission  valve  after  another  is  closed  by  means  of  the  rack 
and  cams,  until  the  proper  speed  is  attained,  when  the  centrifugal  force  of  the  governor-weights 
balances  the  tension  in  the  governor  spring  r.  The  pilot-valve  has  a  very  small  lap,  thus  permitting 
only  a  very  slight  variation  of  speed.  The  sensitiveness  of  the  turbine  depends  on  the  lap  of  the 
pilot-valve. 

Westinghouse  Turbine  Valve-Gear. 

For  illustrating  the  Westinghouse  gear,  their  double-flow  type  of  turbine,  designed  for  large 
powers,  will  be  selected.  A  longitudinal  section  of  this  turbine  is  shown  in  Fig.  148.  The  steam 
inlet  is  at  L,  the  impulse  wheel  at  P  and  the  reaction  blades  at  T,  T.  The  housing  for  the  valves, 


i  xExhanst 

Sectional  View  of  Turbine,  Westinghouse  Double-Flow  Type. 
FIG.  148. 

valve-gears,  etc.,  is  shown  in  section  in  Figs.  149  and  150.  Fig.  151  is  a  diagrammatic  sketch  of 
the  front  elevation  of  the  turbine  showing  the  relative  position  of  the  turbine  housing,  the  valve 
and  the  governor.  A  diagram  of  the  governor  mechanism  and  connections  is  shown  in  Fig.  152. 

The  motion  from  the  governor  comes  through  the  arms  and  links  m,  o,  p,  w,  etc.,  Fig.  151,  to  the 
shaft  D.  The  same  shaft,  D,  is  shown  in  Fig.  150,  and  its  motion  is  transferred  through  the  arm,  E, 
link,  F,  and  floating  lever,  J  G  K,  to  the  pilot-valve,  B,  and  relay  piston  -A.  As  the  turbine  changes 
speed  and  the  governor-weights  move  in  or  out,  the  arm,  E,  is  moved  up  or  down,  and  with  it  the 
point,  J,  of  the  floating  lever  which  turns  momentarily  about  the  point,  K,  thus  carrying  the 
point,  G,  and  the  pilot-valve,  B,  and  admitting  oil  under  pressure  from  the  port,  H,  to  one  side  or 
the  other  of  the  piston,  A,  as  the  regulation  requires.  If,  for  example,  the  piston,  A,  moves  down, 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


123 


it  causes  the  lever,  t  y,  Fig.  149,  to  turn  about  s  and  raise  the  operating  piston,  0,  thus  giving  more 
steam;  at  the  same  time  it  causes  the  lever,  K  J,  Fig.  150,  to  turn  momentarily  about  J,  and  so 
moves  the  pilot-valve,  B,  back  to  its  central  position,  closing  the  oil  ports.  For  any  one  speed  of 
running  the  pilot-valve,  B,  covers  the  ports  of  admission  to  the  two  sides  of  the  piston,  A,  except 
for  a  slight  oscillation,  which  is  described  below,  and  which  allows  the  oil  from  H  to  enter  both  above 
and  below  the  piston,  A,  at  every  cycle.  The  piston,  A,  is  constantly  oscillating  with  a  very  small 
movement,  about  Ji  to  %  of  an  inch. 

The  phase  of  the  valve  mechanism  shown  in  Fig.  150  is  for  full  speed  with  no  load,  or  in  other 
words,  at  the  instant  the  load  is  thrown  off  and  before  the  pilot-valve  has  had  time  to  return  to  its 
neutral  position.  The  arm,  E,  is  full  down  showing  that  the  governor-weights  are  at  full  outward 
swing.  When  the  turbine  is  at  rest,  the  governor-weights  are  at  their  full  inward  positions,  the 
arm,  E,  full  up,  the  pilot-valve  in  its  top  position  with  free  opening  from  H  to  the  top  of  piston,  A, 
and  there  is  no  oil  pressure. 

Upon  starting  the  turbine  the  auxiliary  oil  pump  is  first  set  in  operation,  thus  creating  a  pressure 
in  H  and  driving  oil  through  the  open  port,  B,  causing  the  piston,  A,  to  descend  and  thus  open 


FIG.  149. 


FIG.  150. 


wide  the  primary  valve  0.  Steam  is  then  admitted  by  opening  the  valve  in  the  steam  main,  not 
shown.  The  governor  does  not  "take  hold"  until  the  turbine  has  reached  a  speed  of  about  1400 
r.  p.  m.,  the  rated  speed  for  the  turbine  here  described  being  1800  r.  p.  m.  When  the  turbine  is 
not  in  use  the  valve,  0,  is  kept  to  its  seat  by  the  spring  on  the  valve-stem.  Steam  is  admitted 
through  the  strainer,  Z,  to  the  operating  valve,  0,  and  thence  to  the  turbine  through  the  circular 
opening  represented  by  the  dash-line  circle  also  at  0.  The  valve,  P,  Fig.  149,  is  a  secondary  valve, 
being  designed,  by  means  of  the  adjustable  backlash  device  at  R,  so  that  its  time  of  opening  may 
be  changed  by  the  operator.  It  is  usually  regulated  so  as  to  open  when  the  primary  valve  has 
reached  its  maximum  opening. 

Inasmuch  as  a  governor  must  first  absorb  energy  sufficient  to  overcome  the  friction  of  rest  of 


124 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS 


the  various  movable  parts  of  the  valve-gear  which  remain  stationary  with  respect  to  each  other 
for  any  constant  speed,  it  cannot  instantly"  transmit  the  regulating  motion  for  which  it  is  designed. 
In  order  to  reduce  this  delayed  action,  the  Westinghouse  gear  includes  a  vibratory  motion  illustrated 
in  Fig.  152,  where  it  may  be  seen  that  if  i  were  a  fixed  pivot,  the  lever,  i  j,  would  always  rotate 
about  the  exact  point,  i,  for  each  change  of  speed,  and  the  connecting  link,  i  h,  would  not  be  required. 
At  constant  speed  the  governor-weights,  r  r,  would  then  hold  the  lever,  i  j,  stationary  through  the 
connecting  pin  at  /;  also,  all  the  mechanism  to  and  including  the  valves  would  remain  stationary. 

If,  now,  the  point,  i,  Fig.  152,  is  given  a  slight  vibratory  motion  by  an  eccentric,  c,  the  lever,  i  j, 
will  oscillate  about  the  point,  /,  when  the  turbine  is  running  at  constant  speed,  and  the  valve-gear 
mechanism  will  be  in  constant  motion  and  therefore  more  sensitive,  a  is  a  worm  keyed  to  the 
main  shaft  of  the  turbine  rotor. 

In  the  older  types  of  turbines  of  this  manufacture,  using  steam  instead  of  oil  for  operating  the 


FIG.  151. 


FIG.  152. 


gear,  the  oscillatory  motion  of  i  j  is  transmitted  to  the  pilot-valve,  B,  the  relay  piston,  A,  and  the 
primary  piston  at  0,  thus  admitting  steam  in  a  rapid  series  of  puffs  which  change  according  to  the 
load  as  follows: 

At  light  loads  the  valve,  0,  Fig.  149,  opens  for  a  very  short  period  and  remains  closed  during 
the  greater  part  of  its  cycle.  The  steam  then  enters  in  separate  and  individual  puffs.  As  the  load 
increases  the  period  during  which  the  valve  is  open  increases  also,  until  up  to  about  half-load,  when 
the  valve  ceases  to  close  entirely  and  the  steam  begins  to  have  continuous  admission  to  the  turbine 
although  the  quantity  is  not  constant,  as  the  valve  is  vibrating  near  its  closed  position.  When 
full  load  is  attained,  the  plane  of  vibration  of  the  valve  is  farther  away  from  its  seat  and  the  steam 
enters  in  practically  a  steady  blast. 

In  all  the  larger  sizes  of  Westinghouse  turbines  the  oil  relay  system  is  now  being  used,  and  the 
mechanism  so  designed  that  the  valve,  0,  is  held  practically  stationary  in  its  running  position  so 
that  there  is  very  little  if  any  fluctuation  in  the  steam  pressure  entering  the  turbine. 

The  valve,  0,  is  a  combined  poppet  and  piston-valve,  acting  as  the  former  type  when  it  is  closed 
or  nearly  so,  and  as  the  latter  type  when  it  is  well  open.  An  auxiliary  safety  steam  valve  is  shown 
at  Q  W.  It  is  under  control  of  a  speed-limit  device  and  has  nothing  whatever  to  do  with  the  regular 
running  of  the  turbine.  The  spring  at  X,  Fig.  149,  is  used  to  close  the  primary  valve,  0,  in  case 
of  failure  of  oil  supply,  and  to  keep  it  closed  when  the  turbine  is  not  in  service;  the  spring  at  S,  to 


VALVES,   VALVE-GEARS  AND  VALVE  DIAGRAMS  125 

relieve  the  mechanism  of  strain.  These  are  details  of  construction  which  are  not  essential  to  a 
general  understanding  of  the  turbine  gear  when  running  under  regular  conditions.  It  may  be 
explained,  however,  that  with  the  turbine  at  rest  and  oil  pressure  removed,  the  spring,  X,  will  keep 
the  valve,  0,  closed  and  the  piston,  A,  at  the  top  of  its  stroke.  Also,  with  the  turbine  at  rest,  the 
governor-weights  will  be  full  in,  and  the  lever,  E,  at  its  highest  position,  which  would  cause  a  strain 
on  the  link,  F.  This  strain  is  taken  up  by  the  spring,  S.  In  case  of  failure  of  oil  supply  while  the 
turbine  is  running,  the  spring,  X,  will  close  the  main  valve. 


INDEX 


Actual  steam  velocity 14 

Adjustable  packing-rings    41,  42 

Adjustable  pressure  plate 44 

Admission 5,  8,  9 

Admission,  characteristics   of,    for   reciprocating 

engines  and  for  steam  turbines  119 

Allen  gear   100 

Allen  valve  28,  30,  47,  51 

Allen  valve,  limited  use  of   31 

American-Ball  governor 74,  76 

Angle  between  crank  and  eccentric    3,  6 

Angle  of  advance    3,  7 

Angle  of  advance  for  a  given  cut-off  91 

Angle  of  advance,  effect  of  changing    16 

Angle  of  lap 2 

Angle  of  lead 3 

Angular  accelerating  force   81 

Angularity  of  connecting-rod    i,  4 

Angularity  of  connecting-rod  neutralized.  .23,  64,  85 

Application  of  Zeuner  diagram  7 

Armington  and  Sims  governor  74 

Armington  and  Sims  valve 42 

4"  Atlas  "  valve  68 

Automatic  cut-off  governors  70-82,  119-125 

Auxiliary  ports  47,  48 

Auxiliary  valve  44.  47,  54,  69 

Auxiliary  Zeuner  circles 54 

B 

Baker  valve-gear 109 

Balanced  valve,  locomotive 31,  47 

Balanced  valves   39,  44,  45,  1 10 

Ball  telescopic  valve 45 

Bell  crank  85,  89,  92,  94,  109 

Bilgram  diagram 32 

Box  links  96 

Braemme-Marshall  valve-gear   106 

Bridle  rods 97 

Bridge  wall i 

Bridge  wall  width  19,  51 

Buckeye  governor  73 

Buckeye  valves 69 


Creeping  in  valve-gears  116 

Crossed  rods 88,  89,  100 

Crosshead    i 

Curtis  steam  turbine  valve-gear 119 

Curved-slot   eccentrics    70,  73,  80 

Cushioning  effect  in  dashpots  63 

Cut-off   5,  9 

Cut-off  constant  82 

Cut-off  valves,  or  blocks   44,  47,  50,  54,  69 

Cut-off,  compression  and  release  at 79 

Cut-off,  limit  with  Corliss  gear  61 

Cut-offs  equalized  with  equal  steam-laps  23 

Cut-offs  equalized  with  unequal  steam-laps  ......  19 

Cylinder    center-line    position    relative    to    crank- 
center  15 

Cylinder-head,  valves   in    68 

Cylindrical  rotating  valves 58,  65,  68 

D 

Dashpot  59,  62,  63,  66 

Dead-center    i,   3,  67 

Dead-points  in  valve-gears   66 

Diagram,  Bilgram   32 

Diagram,  Reuleaux   35 

Diagram,  Sinusoidal     38 

Diagram,  valve  ellipse 35 

Diagram,  Zeuner   5 

Distance  blocks 44 

Distribution  valve   47 

Double-bar  links   96 

Double-ported  valves 42-47,  50,  60,  68 

Double-seat  valve  no,  113 

Double  valves   47,  69 

Drafting  table  problem,  No.  i 17 

Drafting  table  problem,  No.  2 28 

Drafting  table  problem,  No.  3 50 

Drafting  table  problem,  No.  4 54 

Drafting  table  problem,  No.  5 64 

Drafting  table  problem,  No.  6 82 

Drafting  table  problem,  No.  7 98 

Drafting  table  problem,  No.  8 116 

D-valve   I,  3,  9,  17 

D-valve,  limited  use  of  27 


Cams  in  valve-gears  no,  113,  120 

Center-lines  in  link-motions 89 

Central  position  of  valve  3,  8,      9 

Classification  of  eccentrics 70 

Classification  of  links 96 

Classification  of  valves 40,    47 

Combination  lever 109 

Compound  engine  valve,  Vauclain 43 

Compound  radial  valve-gears  107 

Compression  ; 5,      8 

Compression  at  early  cut-offs 79 

Compression  equalized  by  unequal  exhaust-laps...     19 
Compression     from     straight-     and     curved-slot 

eccentrics    . '. 80 

Connecting-rods,  angularity  neutralized. ..  .23,  64,    85 

Connecting-rods,  effect  of  angularity 4 

Connecting-rods,  finite  and  infinite 4,  36,     38 

Connecting-rods,  length  of 5 

Constant  lead   76,  81,   100,  103,  no 

Corliss  governor  82 

Corliss  valve   59,    68 

Corliss  valve-gear   59 

Crank-end    I 


Early  cut-offs,  effect  of   79 

Eccentric  positions  and  Zeuner  diagrams   70 

Eccentric  radius  I 

Eccentric  rod  length   5 

Eccentric  rods,  open  and  crossed   88,  98,  100 

Eccentric  sheave    i 

Eccentric  strap   i 

Eccentric  ( throw    65 

Eccentric,  link  equivalent  to  85 

Eccentric,  virtual    . .  .' 85,  98 

Eccentricity   19 

Eccentrics   70,  73,  80,  82;  84 

Eccentrics  and  indicator  cards    79 

Effect  of  angularity  of  connecting-rod 4 

Effect  of  changing  angle  of  advance,  etc 16 

Effect  of  double  or  multiple  ports   29,  50 

Effect  of  friction  due  to  pressure  on  valves 39 

Effect  of  rockers  on  steam  distribution 23,  25 

Effect  of  short  eccentric  rods   88 

Effective  eccentric  arm   2,  3 

Elementary  valve 2,  9,  109 

Elevator  gears   114 

Ellipse,  valve   35 


128 


INDEX 


PAGE 

Engine  parts,  names  of   I 

Envelopes  of  link  center-lines   85,  87 

Equalizing  all  stroke  events  with  a  symmetrical 

valve 27 

Equalizing  compression  with  unequal  exhaust  laps  19 

Equalizing  cut-off  with  equal  steam-laps 23 

Equalizing  cut-off  with  unequal  steam-laps 19 

Equalizing  cut-offs  at  all  gears  with  link-motion.  93 

Equalizing  release  and  exhaust-closure   20,  21 

Examples  of  practical  valve  construction 68 

Exercise  drills  on  Zeuner  diagram  10,  n 

Exercise  problems  on  Zeuner  diagram 12,  28 

Exhaust  5,  8 

Exhaust  closure  9 

Exhaust  lap   4,  9,  10,  19,  80 

Exhaust  lap  circle,  exact  determination  of 18 

Exhaust  lap,  effect  of  changing  16 

Exhaust  lap,  negative   9,  10,  80 

Exhaust  lap,  positive   9 

Exhaust  lap,  zero   9 

Exhaust  lead  10 

Exhaust  opening    8,  10 

Exhaust  pipe    2,  3,  15 

Exhaust  port    2,  3,  15 

Exhaust  port  opening,  maximum  10 

Exhaust  port,  formula  for  width  of  19 

Expansion  5,  8 


Finite  connecting-rod   4 

Fink  gear   101 

Fitchburg  governor    75 

Fitchburg  valve 43 

Fixed  eccentric 70 

Fixed  pressure-plate  44 

Flexible  pressure-plate   45 

Floating  lever 1 14,  1 16,  1 19,  122 

Floating  valve-gear  114,  116,  119,  122 

Forbes  piston-valve   40 

Forces  used  in  shaft-governors   81 

Formula  for  live  and  exhaust  steam-ports 14 

Formula  for  steam-lap 12 

Formula  for  width  of  bridge  19 

Formula  for  width  of  exhaust-port  19 

Forward  stroke  i 

Friction  of  valve  on  seat  39 

Full  exhaust  opening  8,     10 


Gonzenbach  valve 47-49,  69 

Gooch  valve-gear   100 

Governor,  American-Ball    74,  76 

Governor,  Armington  and  Sims 74 

Governor,  Buckeye    73 

Governor,  Corliss   82 

Governor,  Curtis  steam  turbine  119 

Governor,  delayed  action  of,  due  to  friction 123 

Governor,  Fitchburg 75 

Governor,  gravity  balance  76 

Governor,  inertia  81 

Governor,  Lentz    114 

Governor,  revolving  pendulum  82 

Governor,  "  Straight  Line  "  73 

Governor,  throttling    82,  121 

Governor,  Watertown    77 

Governor,  Westinghouse  engine    73 

Governor,  Westinghouse  steam  turbine 122 

Governors,  automatic  cut-off  70-82,  119-125 

Governors,  shaft-  73-75,  81,  82 

Grab-hook,  Corliss 60 


Gravity  balance  in  governors  76 

Gridiron  valve  69 

H 

Hackworth  valve-gear 105 

Half  valve-travel   4 

Hanger    85,  89 

Head  end  ..  I 


"  Ideal  "  piston-valve  42 

Indicator  card  and  valve  ellipse  combined 36 

Indicator  cards,  using  different  eccentrics  79 

Indicator  cards,  using  open  and  crossed  rods 98 

Inertia  governors    81 

Inertia  ring  114 

Infinite  connecting-rod   4,  36,  38 

Inside  lap 4 


Joy  valve-gear 107 

K 
Knock-off  cam  block  .  60 


Lap  and  lead  lever 103 

Lap  angle  2 

Lap  circle,  trial    I7>  J8 

Lap  plus  lead  circle  87 

Lap  thickness 20 

Lap,  exhaust 4,  9,  *o,  19,  So 

Lap,  inside    4 

Lap,  outside  4»  9- 

Lap,  steam  2 

Layout  of  valve-seat  and  valve  18 

Lay  shaft 113 

Lead   3,  & 

Lead  angle  3 

Lead  for  open  and  crossed  rods  88 

Lead  for  link-motions    87,  95 

Lead,  amount  of  3 

Lead,  constant   76,  81,  100,  103,  no 

Lead,  effect  of  multiple-ports  on 29 

Lead,  exhaust  10 

Lead,  port  opening  equal  to  8,  86 

Length  of  connecting-rod 5 

Length  of  eccentric-rod    5 

Length  of  port 15,  62 

Lentz  valve-gear  113 

Limited  use  of  Allen  valve   31 

Limited  use  of  D-yalve    27 

Limit  of  cut-off  with  Corliss  gear  61 

Limit  of  speed  with  Corliss  gear  62 

Liners  for  valves   40 

Link  block  .: 98 

Link  equivalent,   at   any   one   setting,   to   curved- 
slot  eccentric 85 

Link-motions  •.•••; 84-103 

Link-motions,  position  of  center-line  in 89 

Link-travel 95 

Links,  classification  of   96 

Locomotive  balanced  valve 31,  47 

Locomotive  running  under   I 

Locomotive  valve-gears   84,  109 

M 

Main  valve 47,  So,  69 

Marine  engine  valve-gear 84,  97 


INDEX 


129 


PAGE 

Marshall  valve-gear  106 

Maximum  exhaust  port  opening 10 

Maximum  piston  velocity 14 

Maximum  port  opening  8,  19 

Maximum  steam  velocity  14 

Mclntosh,  Seymour  valve   69 

Meyer  valve   47.  So,  54~58 

Mid-gear  travel  in  link-motions    90 

Models,  use  of,  in  valve-gear  design  :66,  96 

Multiple  ports    29,  50 

Multiple  valve    121 

N 

Names  of  engine  parts .. i 

Negative  exhaust-lap  9,  IO.  80 

Notch 85 

Notebook  problems 15 

O 

Oil  pressure  for  regulating  valves • 122,  124 

Open  links   96 

Open  rods 88,  98,  100 

Operation  of '  steam-engine  2 

Operation  of  steam  turbine,  Curtis 121 

Operation  of  steam  turbine,  Westinghouse   123 

Oscillating  piston    123 

Outside  lap  4,  9 

Over,  running  i,  71 

Overtravel i3i  J9 


Packing-rings  for  valves 4l>  42 

Passageways  in  valves 53 

Pendulum,  revolving  82 

Pfeiffer's  formula  for  steam-lap 12 

Phases  of  steam-engine  cycle  9 

Pilot  valve 122 

Piston  valves  4O-43,  69 

Piston  velocity  14,  62 

Piston,  oscillating  123 

Piston,  relay  122,  124 

Plain  D-valve  . . .  i,  3,  9,  18,  27 

Polonceau  valve  47,  50,  69 

Poppet  valve no,  113,  120,  124 

Port  opening  calculations  for  multi-ported 

valves  28,  29 

Port  opening  calculations  for  single-ported 

valves  13,  X4 

Port  opening  equal  to  lead  8,  86 

Port  opening  in  link-motions  87 

Port  opening,  maximum  8,  19 

Port  width  , 13 

Porter-Allen  valve-gear  102 

Ports,  length  of  15,  62 

Positive  exhaust-lap 9 

Preadmission 79,  80,  no 

Pressure  on  crosshead  guide I 

Pressure-plate  valves 43,  45 

Primary  valve 123,  124 

Problem,  design  of  Stephenson  gear  90 

Problems  involving  eccentric  positions  and  Zeuner 

diagram 7° 

Problems,  drafting  table..  17,  28,  50,  54,  64,  82,  98,  116 

Problems,  exercise 12,  28 

Problems,  notebook  15 

R 

Radial  valve-gears  104,  107 

Radius  rod 59,  97,  100 

Rate  of  change  of  rotation  81 


Rate  of  rotation 81 

Ratio    of    average    to    maximum    steam    velocity 

through  ports   14 

Ratio  of  connecting-rod  to  crank  lengths 5 

Ratio  of  eccentric-rod  to  eccentric  radius  lengths  5 

Ratio  of  lap  to  port  opening 4,  16,  17 

Relation  between  steam-lap  and  cut-off 27 

Relative  valve  circles 55 

Relay  piston 122,  124 

Release  5,  9 

Release  and  exhaust-closure  equalized  20,  21 

Release  at  early  cut-off 79 

Releasing  gear,  Corliss  60 

Return  crank   103,  109 

Return  stroke   i 

Reuleaux  diagram 35 

Reversing  by  use  of  eccentrics   70,  75 

Reversing  by  use  of  gears 84-119 

Reversing  engine  114 

Reversing  lever  85,  109 

Revolving  pendulum 82 

Rocker-arms,  bent  64 

Rocker-arms,  types  of 23 

Rock  shaft 82,  97,  1 10,  114 

Rolling-mill  engine-gears   84 

Rotating  eccentric  70,  73,  82-84 

Rotating  valve   58,  65,  68 

Rotation,  direction  of   i 

Running  ahead  and  astern  112 

Running  over    i,  71 

Running  under    i,  71 


"  S,"  value  of,  in  Meyer  valve 56 

Saddle  block 85,  87,  88,  92 

Scales  used  in  problems  18 

Secondary  valve   123 

Self-centering  valve 114,  116,  119,  122 

Setting  Corliss  valve-gear  62 

Shaft-governors    73~75,  81,  82 

Shifting  links   96 

Short  eccentric-rods 88 

Sinusoidal  diagram 38 

Skeleton  link 96 

Skinner  valve  45 

Slide  bar  105 

Slide  block  85,  88,  100,  113 

Slip  in  link-motions   87,  95,  103 

Slotted  eccentric   .' 70 

Special  valve  exercise  28 

Stationary  engines    i 

Stationary  links   96 

Stationary  piston  63 

Steam-chest   2 

Steam  distribution,  effect  of  rocker  on 23,  25 

Steam-engine,  method  of  operating  2 

Steam-hammer  valve-gear  114 

Steam-lap  2 

Steam-lap,  effect  of  changing 16 

Steam-lap,  formula  for 12 

Steam-lap,  to  find 1 1 

Steam-lap,  trial 17,  18 

Steam-pipes 13 

Steam-port  2 

Steam-port  opening,  area  of   13,  14 

Steam-port  opening,  maximum    8,  19 

Steam-ports,  area  of 13,  14 

Steam  turbine  valve-gears  119-125 

Steam  turbine,  method  of  operating 121,  123 


130 


INDEX 


Steam  velocity  13-1 5,  62,    64 

Steering  gear 114,  1 16 

Stephemon  gear  84-99,  114 

Stevens  gear 1 10 

"  Straight  Line  "  governor  73 

"  Straight  Line  "  valve    43 

Straight  slot  eccentric 70-75,  80,  82-84,   no,  114 

Suspension   rod    100 

Swinging  eccentrics   70,     73 

Swinging  pivots  74 


Table  of  data  and  results,  Problem  I -.  20 

Tangential  accelerating  force   81 

Telescopic  valve,  Ball  45 

Template    85,  87,  91 

Thickness  of  bridge    19,  51 

Thickness  of  lap  projection   20 

Thickness  of  valve  wall   20,  52 

Throttling  governors   82,  121 

Travel  of  valve   4,  18,  19,  41 

Trial  steam  lap  circles    17,  18 

"  Trick  "  valve   28 

Tumbling  shaft   93 

Types  of  eccentrics 71-79 

Types  of  links    96 

Types  of  rocker-arms   23 

Types  of  valve-gears 84-125 

Types  of  valves  39,  47,  68 

U 

Under,  running  i,  .  71 

Unsymmetrical  valve-travel  due  to  rocker 25 

V 

Valve  diagrams 5-9,  32-39 

Valve  ellipse   35 

Valve  exercise,  special    28 

Valve-gears    84-125 

Valve  lap  thickness   20 

Valve  liner    40 

Valve  on  center 3,  8,  9 

Valve  problems 17,  28,  50,  54,  64,  82,  98,  116 

Valve  travel  4,  18,  19,  41 

Valve  travel  due  to   rocker   25 

Valve  travel  of  rotating  valves    65,  69 

Valve  travel  of  sliding  valves 1,4,  18,  19 

Valve  travel,  effect  of  changing  16 

Valve  wall  thickness 20,  52 

Valve,  Allen    28,  30,  47,  51 

Valve,  Armington  and  Sims 42 

Valve,  "  Atlas  "    68 

Valve,  auxiliary  44,  47,  54,  69 

Valve,  Ball  telescopic 45 

Valve,  Buckeye    , 69 

Valve,  Corliss  59-68 

Valve,  double  47,  69 

Valve,  double-seat no,  113 

Valve,  elementary  2,  9,  109 

Valve,  Fitchburg  43 

Valve,  Forbes   40 

Valve,  Gonzenbach' 47~49,  69 

Valve,  Gridiron    69 

Valve,  "  Ideal  "    42 

Valve,  locomotive  balanced    31,  47 

Valve,  Mclntosh,  Seymour   69 

Valve,  Meyer   47,  50,  54-58 

Valve,  pilot   122 

Valve,  plain   D-    i,  3,  9,   18,  27 


Valve,  Polonceau  . : 47,  50,  69 

Valve,  poppet no,  113,  120,  124 

Valve,  primary  123,  124 

Valve,  secondary  123 

Valve,  Skinner 45 

Valve,  "  Straight  Line  "  43 

Valve,  "  Trick  " 28 

Valve,  Vauclain  43 

Valve,  Wheelpck  69 

Valves  in  cylinder  heads  68 

Valves,  balanced 39,  44,  45,  no 

Valves,  classification  of 40,  47 

Valves, 'cut-off  44,  47,  54,  69 

Valves,  cylindrical  rotating  58,  65,  68 

Valves,  double-ported  42-47,  50,  60,  68 

Valves,  piston  40-43,  69 

Valves,  pressure-plate  43,  45 

Valves,  types  of  39,  47,  68 

'  Valve-gear,  Allen  100 

Valve-gear,  Baker  109 

!.  Valve-gear,  Corliss  59 

Valve-gear,  Curtis  steam  turbine 119 

Valve-gear,  Fink  101 

Valve-gear,  floating,  or  self-centering.  114,  116,  119,  122 

Valve-gear,  Gooch  100 

Valve-gear,  Hackworth  105 

V,  Valve-gear,  Joy 107 

v  Valve-gear,  Lentz  113 

Valve-gear,  locomotive  84,  109 

Valve-gear,  Marshall  106 

Valve-gear,  Porter-Allen  102 

Valve-gear,  radial 104 

Valve-gear,  Stephenson 84 

Valve-gear,  Stevens  no 

Valve-gear,  Walschaert 103 

Valve-gear,  Westinghouse  steam  turbine 122 

Vauclain  valve  43 

Velocity  of  exhaust  steam  13,  62 

Velocity  of  live  steam  13-15,  62,  64 

Velocity  of  live  steam  through  ports,  actual 14 

Velocity  of  live  steam  through  ports,  average...  14 

Velocity  of  live  steam  through  ports,  maximum.  14 

Velocity  of  piston  14,  62 

Vibrating  link  105 

Virtual  eccentric  85,  98 

W 

Walschaert  valve-gear 103 

Watertown  shaft-governor '.  77 

Weigh  shaft  97 

Westinghouse  shaft-governor  73 

Westinghouse  steam  turbine  valve-gear  122 

Wheelock  valve  69 

Width  of  bridge   19,  Si 

Width  of  cut-off  blocks  48,  So,  57 

Width  of  exhaust-port  19,  Si 

Wrist  plate 59 


Zero  exhaust  lap    9 

Zeuner  circle    7 

Zeuner  circle  changed  by  rocker 25 

Zeuner  circles,  location  of 10 

Zeuner  diagram   5 

Zeuner  diagram,  application  of 7 

Zeuner  diagram,  effect  of  multiple  ports  on 29 

Zeuner  diagram,  exercises 10,  11 

Zeuner  diagram,  problems    12,  28 

Zeuner  diagrams  for  different  eccentric  positions  70 


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